qtui: Destroy main window before QApplication::quit

This works around a Qt 6 bug(?) that was causing the event
dispatcher loop never to exit after a MainWindow::closeEvent().

Author: jlindgren90

src/qtui/qtui.cc

@@ -46,6 +46,7 @@ class QtUI : public audqt::QtIfacePlugin
         audqt::init();
         aud_config_set_defaults("qtui", qtui_defaults);
         window = new MainWindow;
+        QObject::connect(window, &QObject::destroyed, audqt::quit);
         return true;
     }
 
@@ -60,6 +61,9 @@ class QtUI : public audqt::QtIfacePlugin
 
     void show(bool show)
     {
+        if (!window)
+            return;
+
         window->setVisible(show);
 
         if (show)
@@ -72,7 +76,8 @@ class QtUI : public audqt::QtIfacePlugin
     void quit()
     {
         window->teardown();
-        audqt::quit();
+        window->deleteLater();
+        window = nullptr;
     }
 };