Fix 1800324: closing a window while an animation is playing crashes studio, so don...

Fix 1800324: closing a window while an animation is playing crashes studio, so don't let the window close if it's playing.  Instead we display a message explaining why the window won't close.  It would be better if we could somehow cause the playback to stop and then close the window, but this is better than crashing.

git-svn-id: http://svn.voria.com/code@738 1f10aa63-cdf2-0310-b900-c93c546f37ac