If all tables are skipped it would be impossible to encode any
"non black" video.

Fixes: Timeout (78sec -> 1ms)
Fixes: 15821/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SMACKER_fuzzer-5652598838788096

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>