Do not read strd chunk in avi files as H264 extradata.

Fixes ticket #2561.

libavformat/avidec.c

@@ -713,7 +713,9 @@ static int avi_read_header(AVFormatContext *s)
             }
             break;
         case MKTAG('s', 't', 'r', 'd'):
-            if (stream_index >= (unsigned)s->nb_streams || s->streams[stream_index]->codec->extradata_size) {
+            if (stream_index >= (unsigned)s->nb_streams
+                || s->streams[stream_index]->codec->extradata_size
+                || s->streams[stream_index]->codec->codec_tag == MKTAG('H','2','6','4')) {
                 avio_skip(pb, size);
             } else {
                 uint64_t cur_pos = avio_tell(pb);