Blender Git Loki

Fix T45555 crash with subsurf edge drawing.

Loose edge count was double. It didn't fail on own
tests because they had a small number of loose edges,
but for bigger meshes it hit garbage indices at draw time
and crashed.

Also cleaned up the code to make it less verbose and easier to
understand how indices are counted.

Hope it's the last edge-related fix (fingers crossed)