Quick fix attempt for issue #4076.

This patch attempts to keep the printer access code from being cleared
erroneously on a lost or failed connection.  This only applies to LAN
mode.

Notes:
  - The setting is 'access_code'.  There is also a setting named
    'user_access_code', but it's function is unclear and may be
    vestigal.
  - Some parts of the network connection behavior are handled by the
    networking plugin.  I can't seem to make the machine list refresh
    from outside.

src/slic3r/GUI/GUI_App.cpp

@@ -2072,11 +2072,12 @@ void GUI_App::init_networking_callbacks()
                                 event.SetString(obj->dev_id);
                                 GUI::wxGetApp().sidebar().load_ams_list(obj->dev_id, obj);
                             } else if (state == ConnectStatus::ConnectStatusFailed) {
-                                obj->set_access_code("");
-                                obj->erase_user_access_code();
+                                m_device_manager->localMachineList.erase(obj->dev_id);
                                 m_device_manager->set_selected_machine("", true);
                                 wxString text;
                                 if (msg == "5") {
+                                    obj->set_access_code("");
+                                    obj->erase_user_access_code();
                                     text = wxString::Format(_L("Incorrect password"));
                                     wxGetApp().show_dialog(text);
                                 } else {
@@ -2085,9 +2086,9 @@ void GUI_App::init_networking_callbacks()
                                 }
                                 event.SetInt(-1);
                             } else if (state == ConnectStatus::ConnectStatusLost) {
-                                obj->set_access_code("");
-                                obj->erase_user_access_code();
-                                m_device_manager->localMachineList.erase(obj->dev_id);
+                                //obj->set_access_code("");
+                                //obj->erase_user_access_code();
+                                //m_device_manager->localMachineList.erase(obj->dev_id);
                                 m_device_manager->set_selected_machine("", true);
                                 event.SetInt(-1);
                                 BOOST_LOG_TRIVIAL(info) << "set_on_local_connect_fn: state = lost";