Blender Git Loki

Fix T74438: Vertex-only meshes disappear in wireframe mode

The problem happens because, in wireframe mode, `bool use_wire` is
always `true`, so the function that draws all edges is the called.

The solution is set `use_wire` as `false` when the mesh has no edges.

This matches the behavior of blender 2.79.

Reviewed By: fclem, brecht

Differential Revision: https://developer.blender.org/D7041