FIX:fixed appconfig is not saved when switching dark mode

Change-Id: I77fc3808309a23497000c34b6047a359d12c4622

src/slic3r/GUI/ModelMall.cpp

@@ -165,6 +165,7 @@ namespace GUI {
 
     void ModelMallDialog::on_show(wxShowEvent& event)
     {
+        wxGetApp().UpdateFrameDarkUI(this);
         if (event.IsShown()) {
             Centre(wxBOTH);
         }