Fixed crash in WindowHandler

src/Comet/Maui/CometWindow.cs

@@ -27,5 +27,32 @@ namespace Comet
 
 
 		public string Title => this.Content.GetTitle();
+
+		IWindowHandler windowHandler;
+
+		bool SetViewHandler(IWindowHandler handler)
+		{
+			if (windowHandler == handler)
+				return false;
+			InvalidateMeasurement();
+			var oldViewHandler = windowHandler;
+			//viewHandler?.Remove(this);
+			windowHandler = handler;
+			if (windowHandler?.VirtualView != this)
+				windowHandler?.SetVirtualView(this);
+			if (ReplacedView != null)
+				((IElement)ReplacedView).Handler = handler;
+			//AddAllAnimationsToManager();
+			return true;
+
+		}
+
+
+
+		IElementHandler IElement.Handler
+		{
+			get => this.ViewHandler;
+			set => SetViewHandler((IWindowHandler)value);
+		}
 	}
 }