MetaDataSyncer.isHavenaskShardChanged方法会返回NPE，导致节点失联

[weizijun]

NPE报错如下：

failed to apply updated cluster state in [0s]:
version [1384], uuid [EKfudtDyTUaGBkXNzEr3zg], source [becoming candidate: joinLeaderInTerm]
java.lang.NullPointerException: null
        at org.havenask.engine.MetaDataSyncer.isHavenaskShardChanged(MetaDataSyncer.java:649) ~[?:?]
        at org.havenask.engine.MetaDataSyncer.shouldUpdateQrs(MetaDataSyncer.java:333) ~[?:?]
        at org.havenask.engine.MetaDataSyncer.applyClusterState(MetaDataSyncer.java:320) ~[?:?]
        at org.elasticsearch.cluster.service.ClusterApplierService.callClusterStateAppliers(ClusterApplierService.java:535) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.cluster.service.ClusterApplierService.callClusterStateAppliers(ClusterApplierService.java:526) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.cluster.service.ClusterApplierService.applyChanges(ClusterApplierService.java:496) ~[elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.cluster.service.ClusterApplierService.runTask(ClusterApplierService.java:439) [elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.cluster.service.ClusterApplierService$UpdateTask.run(ClusterApplierService.java:179) [elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:684) [elasticsearch-7.10.0.jar:7.10.0]
        at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.runAndClean(PrioritizedEsThreadPoolExecutor.java:252) [elasticsearch-7.10.0.jar:7.10.0]

[Huaixinww]

fixed by:#349