Fix ODBC Hook sql select return empty table

[roel-w]

When querying using a select statement with the odbc hook and the return is an empty table (sqlalchemy []).

File "/usr/local/lib/python3.9/site-packages/airflow/providers/odbc/hooks/odbc.py", line 219, in _make_serializable
    columns: list[tuple[str, type]] = [col[:2] for col in result[0].cursor_description]
IndexError: list index out of range

because of result[0]
This early return fixes this issue.

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[boring-cyborg]

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