riff: retry reading metadata without padding if it fails with

Fixes Ticket1821

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/riff.c

@@ -768,12 +768,17 @@ int ff_read_riff_info(AVFormatContext *s, int64_t size)
         char key[5] = {0};
         char *value;
 
+        chunk_code = avio_rl32(pb);
+        chunk_size = avio_rl32(pb);
+        if (chunk_size > end || end - chunk_size < cur || chunk_size == UINT_MAX) {
+            avio_seek(pb, -9, SEEK_CUR);
             chunk_code = avio_rl32(pb);
             chunk_size = avio_rl32(pb);
             if (chunk_size > end || end - chunk_size < cur || chunk_size == UINT_MAX) {
                 av_log(s, AV_LOG_ERROR, "too big INFO subchunk\n");
                 return AVERROR_INVALIDDATA;
             }
+        }
 
         chunk_size += (chunk_size & 1);