[Painless Lab] UI freezes when using filter context

[cjcenizal]

To reproduce, attempt to send this request with the UI:

PUT /my-index
{
  "mappings": {
    "properties": {
      "field": {
        "type": "keyword"
      }
    }
  }
}

POST /_scripts/painless/_execute
{
  "script": {
    "source": "doc['field'].value.length() <= params.max_length",
    "params": {
      "max_length": 4
    }
  },
  "context": "filter",
  "context_setup": {
    "index": "my-index",
    "document": {
      "field": "four"
    }
  }
}

The UI will freeze as you edit the Document field.

[elasticmachine]

Pinging @elastic/es-ui (Team:Elasticsearch UI)

[cjcenizal]

Fixed by b7840ff