snow allows creating large output from tiny input, like other
wavelet codecs

Fixes: Timeout (82sec -> 1.5sec)
Fixes: 9520/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SNOW_fuzzer-6286612576075776

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