False negatives for the OS checksum

[LegacyNsfw]

The OS checksum needs to exclude the parameter and calibration ranges. It currently doesn't exclude them, and a quirk of the checksum math enables it to give true positive results, but at the risk of false negatives.

If the parameter and calibration blocks have valid checksums, the app can still check for a valid OS checksum.

But, if the parameter or calibration blocks have invalid checksums, the app will report an invalid checksum for the OS as well, even if the OS blocks are actually valid.