low_delay / has_b_frames fix

Originally committed as revision 770 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h263.c

@@ -3504,6 +3504,8 @@ int mpeg4_decode_picture_header(MpegEncContext * s)
                 return -1;
             }
         }else{
+            // set low delay flag only once so the smart? low delay detection wont be overriden
+            if(s->picture_number==0)
                 s->low_delay=0;
         }