Fixes: signed integer overflow: 2 * 2132811776 cannot be represented in type 'int'
Fixes: 25722/clusterfuzz-testcase-minimized-ffmpeg_IO_DEMUXER_fuzzer-6221704077246464
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>