Fix T82617: artifacts in Cycles viewport when changing subdivision attributes

The old attributes were not cleared when synchronizing the geometries, this could also lead to crashes in other cases.

Ref T82608.

intern/cycles/blender/blender_mesh.cpp

@@ -1073,10 +1073,12 @@ void BlenderSync::sync_mesh(BL::Depsgraph b_depsgraph, BL::Object b_ob, Mesh *me
     mesh->set_value(socket, new_mesh, socket);
   }
 
+  mesh->attributes.clear();
   foreach (Attribute &attr, new_mesh.attributes.attributes) {
     mesh->attributes.attributes.push_back(std::move(attr));
   }
 
+  mesh->subd_attributes.clear();
   foreach (Attribute &attr, new_mesh.subd_attributes.attributes) {
     mesh->subd_attributes.attributes.push_back(std::move(attr));
   }