avformat/avidec: Skip duplicate strf chunks

Fixes Ticket3119
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avidec.c

@@ -623,6 +623,10 @@ static int avi_read_header(AVFormatContext *s)
                 if (cur_pos < list_end)
                     size = FFMIN(size, list_end - cur_pos);
                 st = s->streams[stream_index];
+                if (st->codec->codec_type != AVMEDIA_TYPE_UNKNOWN) {
+                    avio_skip(pb, size);
+                    break;
+                }
                 switch (codec_type) {
                 case AVMEDIA_TYPE_VIDEO:
                     if (amv_file_format) {