Avoid running On Frame hooks during all popups, not only the "Quit mission" popup.

git-svn-id: svn://svn.icculus.org/fs2open/branches/zookeeper@11199 387891d4-d844-0410-90c0-e4c51a9137d3
Trunk sync r11199.

git-svn-id: svn://svn.icculus.org/fs2open/branches/zookeeper@11200 387891d4-d844-0410-90c0-e4c51a9137d3