Was going to try and fix the stuttering/glitching when changing mods /
adjusting star rating but it's for another day.
This has no functional change, just code quality.
I considered having this just be a straight guard followed by an
early-return, but if that guard ever actually gets hit, things are going
to be severely broken all over, and un-breaking them at that point will
be very annoying, so just going to cross fingers and hope this can be an
assertion forevermore instead.