Description:
------------
php_mysql.dll crashes when mysql_close() is called with no link identifier.

Apache 2.2.10

Running php with only one extension

Reproduce code:
---------------
<?php
mysql_connect("localhost", "username", "password") or
   die("Could not connect: " . mysql_error());

echo 'Connected successfully';
mysql_close();
?> 

Expected result:
----------------
Connected successfully

Actual result:
--------------
php_mysql.dll crashes and the connection is reset.