fix compile error on win

Zhao Yuhang

2023-12-22 0cedc474f38dca024f77ebf1d7ac5bf22c19744a

 examples/mainwindow/mainwindow.h

@@ -28,6 +28,7 @@

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

    Theme currentTheme{};