Don't truncate spline/bezier through mode

Don't truncate the through mode bit in the vertex type during
normalization. Normalization is used to convert different vertex types
to a singular normalized one but the through-mode bit should be preserved.

This only affects (fixes) spline and bezier draw commands. The only thing
that was broken was games that drew splines/beziers with through-mode and
have matricies that differ significantly from the identity (didn't load
identity before drawing).

This should not break anything and fix #5087 .
Merge pull request #5141 from Bigpet/BezierThrough

Don't truncate spline/bezier through mode