top hits: huge number in "size" makes node go OOM even with very few docs

[brwe]

To reproduce, start a node with 1g heap and then:

DELETE test

PUT index/doc/id
{
  "text": "text"
}

POST index/_search
{
  "aggs": {
    "text": {
      "terms": {
        "field": "text",
        "size": 10
      },
      "aggs": {
        "top_hits": {
          "top_hits": {
            "size": 200000000
          }
        }
      }
    }
  }
}

Tested 1.7.0.
While it is not a good idea to retrieve 200000000 documents I would still not expect an OOM with only one document.