Add additional logic when performing the 'BACK' action on a DVD to avoid getting stuck.

[b16ccb6] relaxed the definition of a menu to any time one or more buttons are defined.  This can make it difficult to exit playback with the 'BACK' action if a DVD is authored such that the title or root jump points do not contain buttons (but maybe show several minutes of trailers before getting to the menu).

Fixes #11649