Description:
------------
The basic problem is that PDO core sets the `column_count` to
zero, before the driver specific implementation of `next_rowset`
is called, so the column values are never freed.  Since PDO_ODBC
does not implement `cursor_closer`, the memory leak also happens
when `PDOStatement::closeCursor()` called.

The leaks can be seen when the PDO_ODBC test suite is run on a
debug build on PHP-7.4, and also for PHP-7.3 when run with
valgrind or another leak checker.


Test script:
---------------
php run-tests.php ext/pdo_odbc/tests

Expected result:
----------------
no memory leaks

Actual result:
--------------
<https://ci.appveyor.com/project/php/php-src/builds/29760248/job/qrhd1plp255gxwmy#L4986>