Blender Git Loki

Fix T62305: Unconnected group vector inputs are mapped incorrectly

The issue was that `bNodeSocketValueVector` and `bNodeSocketValueRGBA`
don't store the value at the same location in the struct.

I kept the cases for `SOCK_VECTOR` and `SOCK_RGBA` completely separate
for now, because they only share code by coincidence and not because
they are actually the same. Eventually there could be a "Vector Input"
node similar to the "RGB" node.

Reviewers: fclem

Differential Revision: https://developer.blender.org/D4472