Add missing release_buffer on close

Originally committed as revision 20227 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/4xm.c

@@ -832,6 +832,10 @@ static av_cold int decode_end(AVCodecContext *avctx){
         f->cfrm[i].allocated_size= 0;
     }
     free_vlc(&f->pre_vlc);
+    if(f->current_picture.data[0])
+        avctx->release_buffer(avctx, &f->current_picture);
+    if(f->last_picture.data[0])
+        avctx->release_buffer(avctx, &f->last_picture);
 
     return 0;
 }