Removing redundant assignment

[Sackzement]

Removing a redundant assignment

src/SDL_mixer.c:2104:32: style: Variable 'track->fade_frames' is reassigned a value before the old one has been used. [redundantAssignment]
            track->fade_frames = fadeOut;
                               ^

Introduced in commit:
icculus/SDL_remixer@76ec5d3#diff-66d27914364c2b11bd71a896ac07aca5d1b4cbb91cf4c61aa4ef2b1c093b583cL1131

@@ -1131,12 +1153,15 @@ bool Mix_PlayOnce(Mix_Audio *audio)
 static void HaltTrack(Mix_Track *track, Sint64 fadeOut)
 {
     LockTrack(track);
-    if (fadeOut <= 0) {  // stop immediately.
-        TrackFinished(track);
-    } else {
-        track->fade_frames = fadeOut;
-        track->fade_start_frame = track->position;
-        track->fade_direction = -1;
+    if (track->state != MIX_STATE_STOPPED) {
+        if (fadeOut <= 0) {  // stop immediately.
+            TrackFinished(track);
+        } else {
+            track->total_fade_frames = fadeOut;
+            track->fade_frames = track->total_fade_frames;
+            track->fade_frames = fadeOut;
+            track->fade_direction = -1;
+        }
     }
     UnlockTrack(track);
 }