Fix bug where new sounds didn't overplay old sounds

src/Sound.hs

@@ -39,7 +39,7 @@ New sounds with the same keys as
 already playing sounds are merged as follows:
 
     * '_soundChannel' is set to the old value
-    * if the old '_soundStatus' was 'FadingOut', it set to the new value (can restart playback with 'ToStart')
+    * if the old '_soundStatus' was 'FadingOut', it is set to the new value (can restart playback with 'ToStart')
     * other fields are set to the new value.
 
 In the update: 
@@ -57,8 +57,10 @@ mergeSound :: Sound -> Sound -> Sound
 mergeSound newS oldS 
     | _soundStatus oldS == FadingOut
                 = newS & soundChannel .~ _soundChannel oldS
-    | otherwise = newS & soundChannel .~ _soundChannel oldS
+    | _soundChunkID newS == _soundChunkID oldS
+                = newS & soundChannel .~ _soundChannel oldS
                        & soundStatus  .~ _soundStatus oldS
+    | otherwise = newS & soundChannel .~ _soundChannel oldS
 
 updateSounds :: Ord a => IM.IntMap Mix.Chunk -> M.Map a Sound -> IO (M.Map a Sound)
 updateSounds sd ss = do
@@ -156,8 +158,6 @@ setChannelPos :: Int16 -> Mix.Channel -> MaybeT IO Mix.Channel
 setChannelPos a i = do
     _ <- liftIO $ Mix.effectPosition i a 0 
     return i
-
-
 -----------------------------------------------------------------
 {- | Set the volume for all sound channels.
 Behind the scenes, scales a float [0,1] to an Int [0..128].