ENH:optimize the management of access code

Change-Id: If8a3644207d5bca2bb10f49f8ee251b6b6219ce2

src/slic3r/GUI/GUI_App.cpp

@@ -1724,6 +1724,7 @@ void GUI_App::init_networking_callbacks()
                                 event.SetInt(1);
                                 event.SetString(obj->dev_id);
                             } else if (state == ConnectStatus::ConnectStatusFailed) {
+                                obj->set_access_code("");
                                 obj->set_user_access_code("");
                                 m_device_manager->set_selected_machine("");
                                 wxString text;