Valid-enforcement

Turns out that the only time it actually checked "valid" was when you
didn't have a prevailing mutation-category.  That's a Bug as it
effectively turned generimutagen into categorized mutagen for your
strongest category.

This imposes validity checks throughout the non-targeted mutation
procedure, fixing that bug.
Merge pull request #7988 from KA101/mutationenforcement

Valid-mutation enforcement