winit backend: window.request_redraw() within RedrawRequested not working

[rib]

While investigating a crash in #2 we later saw an issue with window.request_redraw() not working as expected if issued during a RedrawRequested callback:

I.e. This didn't work:

Event::RedrawRequested(_) => {
	(..)
	guard.surface_state.as_ref().unwrap().window.request_redraw();
}

...but adding an if check inside RedrawEventsCleared did the trick

Event::RedrawEventsCleared => {
	let mut guard = app.read().unwrap();
	if let Some(surface_state) = &guard.surface_state {
		guard.surface_state.as_ref().unwrap().window.request_redraw();
	}
}

Originally posted by @tshrpl in https://github.com/rib/android-activity/issues/2#issuecomment-1137457821