Coverity 1093637: "fix" out of bounds read of Weapon_info[Weapons[other_obj->instance].weapon_info_index].subtype

(fix for release, at least, Assert probably handles this in debug)

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@9906 387891d4-d844-0410-90c0-e4c51a9137d3