WorldInspectorGui panics if no PrimaryWindow is present

[MWFIAE]

If you configure the WindowPlugin to not close the app if the PrimaryWindow is closed the world inspector gui will panic as it can't retrieve the window.

Configuring the WindowPlugin:

    .add_plugins(DefaultPlugins.set(WindowPlugin{
        exit_condition: ExitCondition::DontExit,
        ..Default::default()
    }))

Panic after closing the window:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: NoEntities("bevy_ecs::query::state::QueryState<&bevy_egui::EguiContext, bevy_ecs::query::filter::With<bevy_window::window::PrimaryWindow>>")', C:\<redacted>\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bevy-inspector-egui-0.18.3\src\quick.rs:80:10

This should be a fairly simple fix, the existing code looks like this:

fn world_inspector_ui(world: &mut World) {
    let mut egui_context = world
        .query_filtered::<&mut EguiContext, With<PrimaryWindow>>()
        .single(world)
        .clone();
    egui::Window::new("World Inspector")
        .default_size(DEFAULT_SIZE)
        .show(egui_context.get_mut(), |ui| {
            egui::ScrollArea::vertical().show(ui, |ui| {
                bevy_inspector::ui_for_world(world, ui);
                ui.allocate_space(ui.available_size());
            });
        });
}

Replacing single with get_single would return a result which can be properly checked without panic :)