Blender Git Loki

Fix for strands undo creating an invalid BMesh.

When copying mesh data to bmesh the MVERT and similar customdata types
have to be omitted. Otherwise the bmesh instance ends up with NULL
pointers in customdata layers, but entries in the typemap != -1. The
effect was that when storing new steps after one or more undo, the
resulting original data would be copied, and subsequent undo steps
are ignored.