TSVB is retaining results even after indexpattern is removed from options

[bhavyarm]

Kibana version: 6.7.0 BC3

Elasticsearch version: 6.7.0 BC3

Server OS version: darwin_x86_64

Browser version: chrome latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): from staging

Describe the bug: I was playing with TSVB and trying to get a top 10 hit on machine.ram on logstash dataset from loading sample data from Kibana tutorial.
https://www.elastic.co/guide/en/kibana/current/tutorial-load-dataset.html

I couldn't get the value for top hit on ram so I deleted the logstash indexpattern and voila - all of a sudden tsvb is displaying the graph, gauge chart and top n for ram that too for a timeperiod which doesn't make sense on the logstash dataset.

This is very confusing and also its letting the user save the chart like this:

[elasticmachine]

Pinging @elastic/kibana-app

[bhavyarm]

These are the es logs:

2019-02-25T14:53:40,510][DEBUG][o.e.a.s.TransportSearchAction] [0zMYHJq] [.monitoring-es-6-2019.02.25][0], node[0zMYHJq-SCC4m4h-CSvFQw], [P], s[STARTED], a[id=5mmgokBrT1Ktvw8f8YIlMQ]: Failed to execute [SearchRequest{searchType=QUERY_THEN_FETCH, indices=[.kibana, .kibana_1, .kibana_task_manager, .monitoring-alerts-6, .monitoring-es-6-2019.02.21, .monitoring-es-6-2019.02.22, .monitoring-es-6-2019.02.23, .monitoring-es-6-2019.02.24, .monitoring-es-6-2019.02.25, .monitoring-kibana-6-2019.02.21, .monitoring-kibana-6-2019.02.22, .monitoring-kibana-6-2019.02.23, .monitoring-kibana-6-2019.02.24, .monitoring-kibana-6-2019.02.25, .reporting-2019.02.17, .security, .security-6, .triggered_watches, .watcher-history-9-2019.02.21, .watcher-history-9-2019.02.22, .watcher-history-9-2019.02.23, .watcher-history-9-2019.02.24, .watcher-history-9-2019.02.25, .watches, bank, heartbeat-6.7.0-2019.02.20, kibana_sample_data_ecommerce, kibana_sample_data_flights, kibana_sample_data_logs, logstash-2015.05.18, logstash-2015.05.19, logstash-2015.05.20, map-test, myindex, shakespeare], indicesOptions=IndicesOptions[ignore_unavailable=true, allow_no_indices=true, expand_wildcards_open=true, expand_wildcards_closed=false, allow_aliases_to_multiple_indices=true, forbid_closed_indices=true, ignore_aliases=false, ignore_throttled=true], types=[], routing='null', preference='null', requestCache=null, scroll=null, maxConcurrentShardRequests=5, batchedReduceSize=512, preFilterShardSize=64, allowPartialSearchResults=true, localClusterAlias=null, getOrCreateAbsoluteStartMillis=-1, source={"size":0,"timeout":"30000ms","query":{"bool":{"must":[{"range":{"@timestamp":{"from":1393358020481,"to":1551124420481,"include_lower":true,"include_upper":true,"format":"epoch_millis","boost":1.0}}}],"adjust_pure_negative":true,"boost":1.0}},"aggregations":{"61ca57f1-469d-11e7-af02-69e470af7417":{"meta":{"timeField":"@timestamp","intervalString":"604800s","bucketSize":604800},"filter":{"match_all":{"boost":1.0}},"aggregations":{"timeseries":{"date_histogram":{"field":"@timestamp","time_zone":"America/New_York","interval":"604800s","offset":0,"order":{"_key":"asc"},"keyed":false,"min_doc_count":0,"extended_bounds":{"min":1393358020481,"max":1551124420481}},"aggregations":{"61ca57f2-469d-11e7-af02-69e470af7417":{"filter":{"exists":{"field":"machine.ram","boost":1.0}},"aggregations":{"docs":{"top_hits":{"from":0,"size":1,"version":false,"seq_no_primary_term":false,"explain":false,"_source":{"includes":["machine.ram"],"excludes":[]},"sort":[{"@timestamp":{"order":"desc"}}]}}}}}}}}}}}] lastShard [true]
org.elasticsearch.transport.RemoteTransportException: [0zMYHJq][127.0.0.1:9300][indices:data/read/search[phase/query]]
Caused by: org.elasticsearch.index.query.QueryShardException: No mapping found for [@timestamp] in order to sort on
	at org.elasticsearch.search.sort.FieldSortBuilder.build(FieldSortBuilder.java:319) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.sort.SortBuilder.buildSort(SortBuilder.java:153) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.metrics.tophits.TopHitsAggregationBuilder.doBuild(TopHitsAggregationBuilder.java:606) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.metrics.tophits.TopHitsAggregationBuilder.doBuild(TopHitsAggregationBuilder.java:63) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AbstractAggregationBuilder.build(AbstractAggregationBuilder.java:139) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AggregatorFactories$Builder.build(AggregatorFactories.java:336) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AggregatorFactory.<init>(AggregatorFactory.java:187) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.bucket.filter.FilterAggregatorFactory.<init>(FilterAggregatorFactory.java:44) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.bucket.filter.FilterAggregationBuilder.doBuild(FilterAggregationBuilder.java:98) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AbstractAggregationBuilder.build(AbstractAggregationBuilder.java:139) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AggregatorFactories$Builder.build(AggregatorFactories.java:336) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AggregatorFactory.<init>(AggregatorFactory.java:187) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.support.ValuesSourceAggregatorFactory.<init>(ValuesSourceAggregatorFactory.java:40) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.bucket.histogram.DateHistogramAggregatorFactory.<init>(DateHistogramAggregatorFactory.java:54) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.bucket.histogram.DateHistogramAggregationBuilder.innerBuild(DateHistogramAggregationBuilder.java:442) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.support.ValuesSourceAggregationBuilder.doBuild(ValuesSourceAggregationBuilder.java:311) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.support.ValuesSourceAggregationBuilder.doBuild(ValuesSourceAggregationBuilder.java:37) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AbstractAggregationBuilder.build(AbstractAggregationBuilder.java:139) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AggregatorFactories$Builder.build(AggregatorFactories.java:336) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AggregatorFactory.<init>(AggregatorFactory.java:187) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.bucket.filter.FilterAggregatorFactory.<init>(FilterAggregatorFactory.java:44) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.bucket.filter.FilterAggregationBuilder.doBuild(FilterAggregationBuilder.java:98) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AbstractAggregationBuilder.build(AbstractAggregationBuilder.java:139) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.aggregations.AggregatorFactories$Builder.build(AggregatorFactories.java:336) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.SearchService.parseSource(SearchService.java:811) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.SearchService.createContext(SearchService.java:620) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.SearchService.createAndPutContext(SearchService.java:595) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.SearchService.executeQueryPhase(SearchService.java:386) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.SearchService.access$100(SearchService.java:125) ~[elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.SearchService$2.onResponse(SearchService.java:358) [elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.SearchService$2.onResponse(SearchService.java:354) [elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.search.SearchService$4.doRun(SearchService.java:1085) [elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) [elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:41) [elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:751) [elasticsearch-6.7.0.jar:6.7.0]
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) [elasticsearch-6.7.0.jar:6.7.0]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167) [?:?]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641) [?:?]
	at java.lang.Thread.run(Thread.java:844) [?:?]

[alexwizp]

Interesting issue. I think it'a a regression issue after #24832 and #30946
Not sure that we should set the empty string as a default value for index_pattern during creating a new TSVB. In case of '' it's very difficult to understand is it a user value or we should replace it to default index pattern.

@timroes @markov00 Please review the PR below.