Playlist Viewer: Delete playlist when emptied
When you removed all tracks from an on-disk playlist,
you were asked whether you wanted to save it, which
would fail, but did not show any accompanying message.
Instead of trying to save the playlist, after getting
the confirmation, delete the playlist file from disk.
Change-Id: Iad54f2f490b15dd9c8a8fdfb8f12e58fd17d5e36