Fix coverity sign extension warning

[weirddan455]

Description

Again, not sure how to test that this actually fixes the warning without pushing to main but I think this one is pretty straight forward.

Related issues

#2996

Manual testing

It builds.

Checklist

Please tick the items as you have addressed them. Don't remove items; leave the ones that are not applicable unchecked.

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[kcgen]

Nice fix, @weirddan455 !