Caused by 6a5c14e58f which still inverted the mask even though
it was being subtracted from the factor, effectively inverting it anyway.
Instead restore the previous logic which gathered the mask before
dealing with visibility. That's preferred because it can be replaced with
a `gather` when mask storage is inverted to be like selection, and
because the logic is a bit simpler. Also remove the clamping of the mask
since it generally shouldn't break sculpt code and because mask values
are clamped by editing tools already.
b0d68627a3