TR1X bug: environment BGM is not saved

[rr-]

I'm not sure if it's a bug or a feature, but the fix is simple:

diff --git a/src/tr1/game/savegame/savegame_bson.c b/src/tr1/game/savegame/savegame_bson.c
index bc06d1f3..36572229 100644
--- a/src/tr1/game/savegame/savegame_bson.c
+++ b/src/tr1/game/savegame/savegame_bson.c
@@ -1248,7 +1248,7 @@ static JSON_OBJECT *M_DumpCurrentMusic(void)
 {
     JSON_OBJECT *current_music_obj = JSON_ObjectNew();
     JSON_ObjectAppendInt(
-        current_music_obj, "current_track", Music_GetCurrentTrack());
+        current_music_obj, "current_track", Music_GetCurrentPlayingTrack());
     JSON_ObjectAppendDouble(
         current_music_obj, "timestamp", Music_GetTimestamp());