Fix incorrect file offsets when exporting PCK

[cgytrus]

rn it uses the argument thats passed to the function instead of the local thats actually updated lol
ive tested this change with one game im REing and can confirm that it has fixed my issue

[nikitalita]

Thanks for the PR! Can you double check that the artifact from the build action fixed the issue?

[cgytrus]

yep, just tested by extracting the pck then packing it back and using --main-pack to load it, loads fine and everything seems to be working correctly

[nikitalita]

thank you!