Fixed|Audio: Map music stops when map reloaded

If the correct music is already playing, it isn’t an error if the same music is requested to be played.

doomsday/apps/client/include/audio/audiosystem.h

@@ -131,11 +131,11 @@ class AudioSystem : public de::System
     /**
      * Start playing a song. The chosen interface depends on what's available and what
      * kind of resources have been associated with the song. Any previously playing song
-     * is stopped.
+     * is stopped. If the song is already playing, no changes are applied.
      *
      * @param definition  Music definition describing which associated music file to play.
      *
-     * @return  Non-zero if the song is successfully played.
+     * @return  Non-zero if the song is successfully played (or already playing).
      */
     int playMusic(de::Record const &definition, bool looped = false);
 

doomsday/apps/client/src/audio/base/audiosystem.cpp

@@ -1759,7 +1759,10 @@ dint AudioSystem::playMusic(Record const &definition, bool looped)
 
     // We will not restart the currently playing song.
     if (definition.gets("id") == d->musCurrentSong && musicIsPlaying())
-        return false;
+    {
+        // This is not a failure, though, since the right music is played.
+        return true;
+    }
 
     // Stop the currently playing song.
     stopMusic();