Cleanup: Missing custom data implicit sharing info in edit mesh undo

The missing sharing info shouldn't cause crashes currently, but since this
is the one place that CustomData is built "manually" it's better to do the
standard thing and create it.

source/blender/editors/mesh/editmesh_undo.cc

@@ -334,6 +334,7 @@ static void um_arraystore_cd_expand(const BArrayCustomData *bcd,
         if (state) {
           size_t state_len;
           layer->data = BLI_array_store_state_data_get_alloc(state, &state_len);
+          layer->sharing_info = implicit_sharing::info_for_mem_free(layer->data);
           BLI_assert(stride * data_len == state_len);
           UNUSED_VARS_NDEBUG(stride, data_len);
         }