USD Export: handle meshes in edit mode.

Small change to ensure Edit mode meshes are committed during the
export process.  Without this change, meshes may be empty in the
USD.  This update was authored by Charles Wardlaw.

source/blender/io/usd/intern/usd_writer_mesh.cc

@@ -19,6 +19,7 @@
 #include "BKE_material.h"
 #include "BKE_mesh.h"
 #include "BKE_mesh_runtime.h"
+#include "BKE_mesh_wrapper.h"
 #include "BKE_modifier.h"
 #include "BKE_object.h"
 
@@ -26,7 +27,6 @@
 #include "bmesh_tools.h"
 
 #include "DEG_depsgraph.h"
-
 #include "DNA_layer_types.h"
 #include "DNA_mesh_types.h"
 #include "DNA_meshdata_types.h"
@@ -504,6 +504,8 @@ void USDGenericMeshWriter::write_mesh(HierarchyContext &context, Mesh *mesh)
   write_visibility(context, timecode, usd_mesh);
 
   USDMeshData usd_mesh_data;
+  /* ensure data exists if currently in edit mode */
+  BKE_mesh_wrapper_ensure_mdata(mesh);
   get_geometry_data(mesh, usd_mesh_data);
 
   if (usd_export_context_.export_params.export_vertices) {