fix possible QWKQuick crash

Zhao Yuhang

2025-05-07 576654b6173e97425411010b2f40b3e9519b85b8

 examples/mainwindow/mainwindow.h

@@ -30,8 +30,6 @@
protected:
    bool event(QEvent *event) override;

    void closeEvent(QCloseEvent *event) override;

private:
    void installWindowAgent();
    void loadStyleSheet(Theme theme);