If you played e.g. an audio-only file and something bad happened that
interrupted playback, the exit message could say "No files played".
This was awkward, so show a different message in this case.
Also overhaul how the exit status is reported in order to make this
easier. This includes things such as not reporting a playback error
when loading playlists (playlists contain no video or audio, which
was considered an error).
Not sure if I'm happy with this, but for now it seems like a slight
improvement.