expand sound:: interface a bit

src/sound.cpp

@@ -486,6 +486,11 @@ void play_no_music()
 	}
 }
 
+void empty_playlist()
+{
+    current_track_list = std::vector<music_track>();
+}
+
 void play_music()
 {
 	music_start_time = 1; //immediate (same as effect as SDL_GetTicks())

src/sound.hpp

@@ -48,8 +48,10 @@ void commit_music_changes();
 void play_music_repeatedly(const std::string &name);
 // Play this particular music file once, then silence.
 void play_music_once(const std::string &name);
-// Empty the playlist.
+// Empty the playlist (and stop playing)
 void play_no_music();
+// Empty the playlist
+void empty_playlist();
 // Start playing current music.
 void play_music();