Smoother MD2 interpolation

Originally fixed by toaster. Fixes a case where animations can end up being jerky(like FSonic's Super Sonic walk animations) In her own words:"The jerkiness was caused by treating all calculations as if interpoleration should be within the bounds, whilst not actually doing anything to limit it to that" Should be safe to merge to master.

https://mb.srb2.org/showpost.php?p=798298&postcount=69