Fix a regression where the login panel is displayed even when the plugin is disabled (#12185)

Update GUI_App to show or hide the login panel based on the "installed_networking" setting.

src/slic3r/GUI/GUI_App.cpp

@@ -4439,7 +4439,11 @@ void GUI_App::get_login_info()
                 GUI::wxGetApp().run_script(strJS);
             }
         }
-        mainframe->m_webview->SetLoginPanelVisibility(true);
+        if(app_config->get_bool("installed_networking")) {
+            mainframe->m_webview->SetLoginPanelVisibility(true);
+        } else {
+            mainframe->m_webview->SetLoginPanelVisibility(false);
+        }
     }
 }