clang-tidy: replace unsigned long with uint64_t
clang-tidy: replace unsigned long with uint64_t

Found with google-runtime-int

Signed-off-by: Rosen Penev <cd9d359349c2d33dfd3bf458517d943871c7c054@gmail.com>

Matroska-Org/libebml,Matroska-Org/libebml