Blender Git Loki

Fix crash on edge extrude from textured view

Issue was caused by MFACE layer adding for even DM without tessellated faces
which lead to adding new layer but with NULL data. This causes issues when layer
with faces (after extrude) was attempting to add because currently CD only checks
if layer type exists but does not check for size of the layer.

Solved by not adding MFACE layer if there's no tessellated faces.