Update dblib_driver.c

Bugfix for issue 63638. The patch from 1 to NULL is reverted with this commit.

Please see: https://bugs.php.net/bug.php?id=63638

This pull request addresses that issue and should be merged.

NOTE: This pull request is for the php5.4.13 branch. The original (https://github.com/php/php-src/pull/306) was for the master branch.