Input source: Update monado devices only if they are available

Fixes .unwrap() panic in the simulated Monado driver

src/backend/openxr/mod.rs

@@ -212,9 +212,11 @@ pub fn openxr_run(running: Arc<AtomicBool>, show_by_default: bool) -> Result<(),
         }
 
         if next_device_update <= Instant::now() {
-            input_source.update_devices(&mut app_state, monado.as_mut().unwrap());
+            if let Some(monado) = &mut monado {
+                input_source.update_devices(&mut app_state, monado);
                 next_device_update = Instant::now() + Duration::from_secs(30);
             }
+        }
 
         if !session_running {
             std::thread::sleep(Duration::from_millis(100));