Fix macOS title bar buttons not displaying properly.

Dylan Liu

2024-05-03 bdc57c6ec9b08f74ca65a06b8496fbaa3268c5fd

 examples/mainwindow/main.cpp

@@ -33,7 +33,9 @@
    MainWindow w;
    w.show();

#if 0
    QMainWindow w2;
    w2.show();
#endif
    return a.exec();
}