Followup fix to mantis 2887 (from MageKing17)

no-collide ship classes would collide unless the no-collide flag was set
in the mission file

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10989 387891d4-d844-0410-90c0-e4c51a9137d3