Fixes: 67492/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-5778297231310848
Fixes: signed integer overflow: 2314885530818453536 + 7782220156096217088 cannot be represented in type 'long'
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>