There is probably a better place to check for this, but better
here than nowhere

Fixes: signed integer overflow: -9223372036824775808 - 86400000000 cannot be represented in type 'long'
Fixes: 50993/clusterfuzz-testcase-minimized-ffmpeg_dem_SBG_fuzzer-6601162580688896

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