Blender Git Loki

Fix T39520, show diffuse not working in dyntopo.

Was marked as a todo in the code.

This does not yet take care of correct display for multi material
meshes, since it would need correct separation of faces during pbvh
creation. Instead we just take material of first face in node and assume
that the rest faces have the same. This will create some funky effects
if one attempts to sculpt in this way.

Note: This does not yet address T39517