The underlying issue is that the loose edge extraction cannot be
threaded. This patch will extract the loose edges during initialization
of the render mesh data.
When working on this patch the mesh_render_data_update was split into
multiple functions to identify what part was failing. These functions
would also help us with debugging.
Reviewed By: Clément Foucault
Differential Revision: https://developer.blender.org/D7962
ab8a691431