See previous commit for partial rationale.
There's an argument to be made about the `NaN`-spreading semantics being
desirable because at least something will loudly fail in that case, but
I'm not so sure about that these days. It feels like either way if
`NaN`s are produced, then things are outside of any control, and chances
are the game can probably continue without crashing. And, this move
reduces our dependence on osuTK, which has already been living on
borrowed time for years now and is only awaiting someone brave to go
excise it.
