avcodec/mpeg4video_parser: Check for extradata parsing failure

Found-by: CSA
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpeg4video_parser.c

@@ -88,6 +88,8 @@ static int mpeg4_decode_header(AVCodecParserContext *s1, AVCodecContext *avctx,
     if (avctx->extradata_size && pc->first_picture) {
         init_get_bits(gb, avctx->extradata, avctx->extradata_size * 8);
         ret = ff_mpeg4_decode_picture_header(dec_ctx, gb);
+        if (ret < 0)
+            av_log(avctx, AV_LOG_WARNING, "Failed to parse extradata\n");
     }
 
     init_get_bits(gb, buf, 8 * buf_size);