Bug 772785 - Quit dialog should exit when all the images in the list...

... have been saved.
No need to keep a list of 0 images when the creator requested a quit or
close-all actions and manually went through the list to save all
remaining images. Yet one can still cancel the quit/close-all action by
hitting Esc (or Cancel button) during the last save, since it is an
idle source action.