Fix for Mantis 2844: AddressSanitizer: heap-buffer-overflow in pilotfile_convert::csg_import_red_alert csg_convert.cpp:438

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@9630 387891d4-d844-0410-90c0-e4c51a9137d3