[BUG] Select * return null for unexpanded object field

[dai-chen]

What is the bug?

SELECT * statement returns null for unexpanded object field.

How can one reproduce the bug?

POST http://localhost:9200/object-test/_doc/
{
  "account.name.first": "John"
}

POST http://localhost:9200/_plugins/_sql
{
  "query": "SELECT * FROM object-test"
}
{
  "schema": [
    {
      "name": "account",
      "type": "object"
    }
  ],
  "datarows": [
    [
      null
    ]
  ],
  "total": 1,
  "size": 1,
  "status": 200
}

What is the expected behavior?

Return the same result as SELECT account.name.first.

What is your host/environment?

• OpenSearch: main branch

Do you have any additional context?

The root cause maybe the same as described here: #1135 (comment)