CGAL Lab - colors get lost when a C3t3 is duplicated

## Issue Details

In CGALLab, create a multi-domain mesh with Mesh_3, select it and click the "duplicate" icon : the colors associated to `Surface_patch_index` get messed up in the duplicate mesh.
The internal `Subdomain_index` remain valid.

## Environment

* Operating system (Windows/Mac/Linux, 32/64 bits): Windows
* CGAL version: master
