Fix #79038: PDOStatement::nextRowset() leaks column values

Fix #79038: PDOStatement::nextRowset() leaks column values

Firstly, we must not rely on `stmt->column_count` when freeing the
driver specific column values, but rather store the column count in
the driver data.  Since the column count is a `short`, 16 bit are
sufficient, so we can store it in reserved bits of `pdo_odbc_stmt`.

Furthermore, we must not allocate new column value storage when the
statement is not executed, but rather when the column value storage has
not been allocated.

Finally, we have to introduce a driver specific `cursor_closer` to
avoid that `::closeCursor()` calls `odbc_stmt_next_rowset()` which then
frees the column value storage, because it may be still needed for
bound columns.