Fix bug of window closing and reshowing

Sine Striker

2024-02-23 6c0043c1e3d97398828fbd56448f1cd8ee201e66

 examples/mainwindow/main.cpp

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

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