avformat/avidec: Use 64bit for frame number in odml index parsing

Fixes: signed integer overflow: 1179337772 + 1392508928 cannot be represented in type 'int'
Fixes: 34088/clusterfuzz-testcase-minimized-ffmpeg_dem_AVI_fuzzer-5846945303232512

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg


Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>