Do something special with empty blocks (goto only)

[bvisness]

These stupid little goto blocks ruin the layout every time:

It may be reasonable to special-case them as basically dummy nodes. They could still be rendered, but just participate in layout differently.

(I will say, this is kind of just another case of test nodes having their output blocks inverted. But also, these little nodes cause lots of problems for layout, especially when the Split Edges pass runs.)