[Doris On Es] Fix assertion failure when docvalue fields is gone

[dh-cloud]

See test case below:

# curl -H "Content-Type: application/json" -XPUT http://10.35.25.164:9222/test_dd?pretty -d '
{
   "mappings": {
      "_doc": {
         "properties": {
            "k1": {
               "type": "long"
            }
         }
      }
   }
}'

# curl -H "Content-Type: application/json" -XPUT http://10.35.25.164:9222/test_dd/_doc/1?pretty -d '{}'

In DEBUG build mode, if we read the es index, RAPIDJSON_ASSERT
will be triggered because hits.hits.fields does not exist.

# curl -H "Content-Type: application/json" -XPOST '10.35.25.164:9222/test_dd/_doc/_search?filter_path=_scroll_id,hits.total,hits.hits._score,hits.hits.fields&pretty' -d '{"query":{"match_all":{}},"stored_fields":"_none_","docvalue_fields":["k1"]}'
{
  "hits" : {
    "total" : 1,
    "hits" : [
      {
        "_score" : null
      }
    ]
  }
}

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[jackwener]

This PR has not been updated for a long time.

There could be many reasons.

If it's caused by there are no maintainers to push or ignore this PR, I'm sorry.

If you contact maintainer or want to continue this PR, feel free to @me or @other maintainers.