Generation of multiply code is zeroing out some components

1. Create a new ShaderGraph
2. add a Color node
3. feed that into a multiply node's A Slot
4. Set the w component of the default input binding for Slot B to 0

The reproduction of this bug is not limited to this permutation of input binding values. You can set any of the other components to any other value to get some odd behavior.

I added the generated shader code and added a note where the bad code is generated. Ctrl-F for "NOTE(wyatt)" or "@matt"