"Start offset differs" errors when checking version 3 compressed pak

[benrg]

Running u4pak.exe check on the pak from RiME (version 1.04, GOG) produces a large number of compression block with index # start offset differes from expected value: # != # (4), where the difference is always 4. This seems to be caused by the next_start_offset setting logic in check.rs. The pak version is 3, and when I manually patch it to 4, u4pak says "All ok" with no warnings. The Python version says "All ok" with no warnings regardless of the pak version.