Fix mid/side stereo buggy output zeroing, fixes issue264 part 2.

Originally committed as revision 15004 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/wmadec.c

@@ -689,18 +689,12 @@ next:
         n4 = s->block_len / 2;
         if(s->channel_coded[ch]){
             ff_imdct_calc(&s->mdct_ctx[bsize], s->output, s->coefs[ch]);
-        }else
+        }else if(!(s->ms_stereo && ch==1))
             memset(s->output, 0, sizeof(s->output));
 
         /* multiply by the window and add in the frame */
         index = (s->frame_len / 2) + s->block_pos - n4;
         wma_window(s, &s->frame_out[ch][index]);
-
-        /* specific fast case for ms-stereo : add to second
-            channel if it is not coded */
-        if (s->ms_stereo && !s->channel_coded[1]) {
-            wma_window(s, &s->frame_out[1][index]);
-        }
     }
 
     /* update block number */