Fixes: signed integer overflow: 904444 * 3600 cannot be represented in type 'int'
Fixes: 15113/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5764083346833408

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