avformat/id3v2: Sanity check tlen before alloc and uncompress

Fixes: Timeout (>20sec -> 65ms)
Fixes: 26896/clusterfuzz-testcase-minimized-ffmpeg_dem_DAUD_fuzzer-5691024049176576
Fixes: 27627/clusterfuzz-testcase-minimized-ffmpeg_dem_AEA_fuzzer-4907019324358656

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit d7f87a4b9e)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/id3v2.c

@@ -993,6 +993,9 @@ static void id3v2_parse(AVIOContext *pb, AVDictionary **metadata,
 
                     av_log(s, AV_LOG_DEBUG, "Compresssed frame %s tlen=%d dlen=%ld\n", tag, tlen, dlen);
 
+                    if (tlen <= 0)
+                        goto seek;
+
                     av_fast_malloc(&uncompressed_buffer, &uncompressed_buffer_size, dlen);
                     if (!uncompressed_buffer) {
                         av_log(s, AV_LOG_ERROR, "Failed to alloc %ld bytes\n", dlen);