A chapter length near INT64_MAX overflowed the rounding, the hour count
was also truncated to int.
Fixes: signed integer overflow
Fixes: 7JHyBJsQ7bNE
Regression since: 80a55704b7
Found during the review of https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24589
Signed integer overflow Replicated through UnModified FFmpeg with UBSAN