Fixes: Timeout (11sec -> 6sec)
Fixes: 16344/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ANM_fuzzer-5673032000995328

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegReviewed-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 1965161e)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>