2989l: Set avctx->has_b_frames value in header and don't change it

Originally committed as revision 6233 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/vc1.c

@@ -4085,6 +4085,7 @@ static int vc1_decode_init(AVCodecContext *avctx)
           return -1;
     }
     avctx->has_b_frames= !!(avctx->max_b_frames);
+    s->low_delay = !avctx->has_b_frames;
 
     s->mb_width = (avctx->coded_width+15)>>4;
     s->mb_height = (avctx->coded_height+15)>>4;
@@ -4145,8 +4146,6 @@ static int vc1_decode_frame(AVCodecContext *avctx,
         s->current_picture_ptr= &s->picture[i];
     }
 
-    avctx->has_b_frames= !s->low_delay;
-
     //for advanced profile we need to unescape buffer
     if (avctx->codec_id == CODEC_ID_VC1) {
         int i, buf_size2;