Fix T87876: vertex groups missing when mesh is in edit mode

Differential Revision: https://developer.blender.org/D11107

source/blender/blenkernel/intern/DerivedMesh.cc

@@ -1603,6 +1603,12 @@ static void editbmesh_calc_modifiers(struct Depsgraph *depsgraph,
   /* This geometry set contains the non-mesh data that might be generated by modifiers. */
   GeometrySet geometry_set_final;
 
+  /* Add the initial mesh component, with a copy of the vertex group names from the object,
+   * since they need to be stored in the geometry set for evaluation. */
+  MeshComponent &initial_mesh_component =
+      geometry_set_final.get_component_for_write<MeshComponent>();
+  initial_mesh_component.copy_vertex_group_names_from_object(*ob);
+
   /* Deformed vertex locations array. Deform only modifier need this type of
    * float array rather than MVert*. Tracked along with mesh_final as an
    * optimization to avoid copying coordinates back and forth if there are