* fixed bug #5065 (ALT-TAB sometimes causes music to spam console )

* the reason was not really the alt+tab but the end of van_theme in the category 'main'. It was the only track and thus
  the cvar snd_music was never really changes (was always the same value). Without the cvar being changed, no new track
  was started.
* snd_music is not always up to date - but music.currentTrack is
* don't skip starting the same track again if we are not playing any music track