Improve combiner overflow behavior

[Dragorn421]

#335 (tried to) improve combiner overflow behavior

but we had to revert it due to breaking preview of other things #347

So that improvement is back on the table

[jesusyoshi54]

So basically the comber C input overflows >= 256, which is only on the 1.0 input, the others are 255 max. I didn't account for this the second time i edited the nodes woopsie.
Somehow I didn't see this when I tested because I only tested that the aberrant behavior was fixed not that all manner of normal behavior still worked.

[Lilaa3]

I only checked the nodes and tested the behavior on a simple black and white material so this is partly my fault, I will try out scenes in any future f3d rendering related PRs, sorry about this.

[jesusyoshi54]

Can someone post some of the combiners of the broken materials shown in #347 I can't quite recreate the extent with which things get messed up.