Fix -playmusic command line option not working

There's a bug where playtesting from Ved doesn't properly play the music
of the level, due to no fault with Ved.

This was because the music was being faded out by
scriptclass::startgamemode() case 23 after main() called music.play().
To fix this, just call music.play() when all the other variables are
being set in Game::customloadquick().

desktop_version/src/Game.h

@@ -387,6 +387,7 @@ public:
     int playrx;
     int playry;
     int playgc;
+    int playmusic;
     std::string playassets;
 
     void quittomenu();