fix(bq_driver): HTAPI fetch results fix when table is empty

[KanchanShu]

Summary

Fix the HTAPI execution path for queries that return an empty result set. Previously, reaching the end of the HTAPI read stream during execution could return SQL_NO_DATA prematurely. This change aligns HTAPI behavior with the existing non-HTAPI flow.

Changes

• Updated ReadNextResultsFromStream() to:

  • Treat end-of-stream as a successful completion during execution.
  • Clear the cached result set and reset the cursor for empty results.
  • Avoid returning SQL_NO_DATA during execution.

• Preserve SQL_NO_DATA generation in the fetch path (FetchNextResultSet()), so it is returned by SQLFetch() when no rows are available.

• Added a test for an empty result set (WHERE 1=2) to verify successful execution and results.size() == 0.

Behavior

Before

• HTAPI could return SQL_NO_DATA during execution for empty result sets.

After

• SQLExecDirect/SQLExecute succeeds for empty result sets.
• SQLFetch returns SQL_NO_DATA when no rows are available.
• Empty queries return results.size() == 0, matching the non-HTAPI behavior.