Fix GH-15432: Heap corruption when querying a vector

Since the mysqlnd result set is arena allocated, we must not simply
free it, but rather call the appropriate `free_result` method.

Fix GH-15432: Heap corruption when querying a vector

Since the mysqlnd result set is arena allocated, we must not simply
free it, but rather call the appropriate `free_result` method.

Co-authored-by: Kamil Tekiela <tekiela246@gmail.com>

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