Fixes: Assertion failure
Fixes: 15151/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5757079496687616
Fixes: 15205/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5767573242642432
May fix: Ticket7094
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>