Fix gcc warning: ordered comparison of pointer with integer zero

git-svn-id: svn://svn.icculus.org/fs2open@10935 387891d4-d844-0410-90c0-e4c51a9137d3
Trunk Sync - r10935

git-svn-id: svn://svn.icculus.org/fs2open@10936 387891d4-d844-0410-90c0-e4c51a9137d3