Fix reading partitions and sector ranges larger than 4 GiB

Fixes: #1 (closed)

Fix was taken from [1] and slightly adapted to match the surrounding naming conventions.

Tested by dumping the full "userdata" partition of my PineNote

[1] https://github.com/tpwrules/nixos-pinenote/blob/96d2c9158edb9da59afcb952cc864fada18382f9/nix/rkdeveloptool/0001-fix-large-dumps.patch