Blender Git Loki

Fix crash using object.to_mesh() when in edit mode

The root of the issue was caused by mesh which was a result of to_mesh()
had the same edit_mesh pointer as the input object, causing double-free
error.

This fix makes it so result mesh does not have edit mesh pointer.
Motivation part behind this is to make the result of to_mesh() to be
somewhat independent from the input.

Differential Revision: https://developer.blender.org/D7361