Blender Git Loki

Viewport: Fix stereoscopy volume "wires" not showing

This is unreported. When using volume opacity 0.0, the wires were not visible
(nor were they in other cases, but this was the most obvious one).

The volume itself is still glitchy, and slightly worse than 2.79. I
still don't know how to fix this though. It seems a common problem
(see T62262).