Fix ordering issues when with_menu(None) is called before setting the window builder

[ealmloff]

This example currently shows the default menu even though the menu is explicitly set to None:

use dioxus::{desktop::WindowBuilder, prelude::*};

fn main() {
    let window = WindowBuilder::new()
        .with_always_on_top(false)
        .with_resizable(false)
        .with_title("Marionette");

    let config = dioxus::desktop::Config::new()
        // The menu is set here
        .with_menu(None)
        // But then reset to the default here
        .with_window(window);
    let launcher = LaunchBuilder::new().with_cfg(config);
    launcher.launch(app);
}

fn app() -> Element {
    rsx! {
        "hello world"
    }
}

This PR fixes that issue