Catch a lua error that apparently can happen


git-svn-id: svn://svn.icculus.org/fs2open@10759 387891d4-d844-0410-90c0-e4c51a9137d3
Fix a few gcc compile errors introduced by r10756

git-svn-id: svn://svn.icculus.org/fs2open@10760 387891d4-d844-0410-90c0-e4c51a9137d3
derp, forgot an else-if

git-svn-id: svn://svn.icculus.org/fs2open@10761 387891d4-d844-0410-90c0-e4c51a9137d3
7-Zip-JBinding can't extract .xz files

git-svn-id: svn://svn.icculus.org/fs2open@10762 387891d4-d844-0410-90c0-e4c51a9137d3
Coverity ID 1221483: Missing break in switch

git-svn-id: svn://svn.icculus.org/fs2open@10763 387891d4-d844-0410-90c0-e4c51a9137d3
Coverity 1221482: Dereference after null check

Stop Ctrl-PgUp/PgDown crashing when a briefing icon is not in closeup mode

git-svn-id: svn://svn.icculus.org/fs2open@10764 387891d4-d844-0410-90c0-e4c51a9137d3