emulate (idiotic) MS behavior for inconsistant dimensions

Originally committed as revision 3940 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h263.c

@@ -5538,7 +5538,7 @@ static int decode_vol_header(MpegEncContext *s, GetBitContext *gb){
             skip_bits1(gb);   /* marker */
             height = get_bits(gb, 13);
             skip_bits1(gb);   /* marker */
-            if(width && height){ /* they should be non zero but who knows ... */
+            if(width && height && !(s->width && s->avctx->codec_tag == ff_get_fourcc("MP4S"))){ /* they should be non zero but who knows ... */
                 s->width = width;
                 s->height = height;
 //                printf("width/height: %d %d\n", width, height);