Left over pointer towards a structure that had been cleared and rebuilt could cause a crash. Found (and fix tested) by Axem. Also thanks to z64555 for bouncing ideas back and forth until this solution was found.
git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@11314 387891d4-d844-0410-90c0-e4c51a9137d3