Fix previous commit:
1) array_key_exist does not exist - it is array_key_exists
2) array_key_exists only works on a single dimension array, so we use current()/is_array to search for the sort column in the array and ensure we have a multi-dimensional array.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@5690 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9