Fix Android crash on resume with Glow backend (#3867)

Addition for <https://github.com/emilk/egui/pull/3847>
In previous one i only fixed crash occurring with Wgpu backend. This
fixes crash with Glow backend as well.
I only tested this change with android so most things i changed are
behind ```#[cfg(target_os = "android")]```.

Both fixes are dirty thought. As
<https://github.com/emilk/egui/pull/3172> says that "The root viewport
is the original viewport, and cannot be closed without closing the
application.". So they break rules i guess? But i can't think about
better solution for now.

Closes <https://github.com/emilk/egui/issues/3861>.

crates/eframe/src/native/glow_integration.rs

@@ -39,18 +39,6 @@ use super::{
     *,
 };
 
-// Note: that the current Glutin API design tightly couples the GL context with
-// the Window which means it's not practically possible to just destroy the
-// window and re-create a new window while continuing to use the same GL context.
-//
-// For now this means it's not possible to support Android as well as we can with
-// wgpu because we're basically forced to destroy and recreate _everything_ when
-// the application suspends and resumes.
-//
-// There is work in progress to improve the Glutin API so it has a separate Surface
-// API that would allow us to just destroy a Window/Surface when suspending, see:
-// https://github.com/rust-windowing/glutin/pull/1435
-
 // ----------------------------------------------------------------------------
 // Types:
 
@@ -525,7 +513,9 @@ impl GlowWinitRunning {
             let mut glutin = self.glutin.borrow_mut();
             let egui_ctx = glutin.egui_ctx.clone();
             let viewport = glutin.viewports.get_mut(&viewport_id).unwrap();
-            let window = viewport.window.as_ref().unwrap();
+            let Some(window) = viewport.window.as_ref() else {
+                return EventResult::Wait;
+            };
             egui_winit::update_viewport_info(&mut viewport.info, &egui_ctx, window);
 
             let egui_winit = viewport.egui_winit.as_mut().unwrap();