Move TryGetPlatformHandle to TopLevel Fix

src/Avalonia.Controls/TopLevel.cs

@@ -383,7 +383,7 @@ namespace Avalonia.Controls
         /// An <see cref="IPlatformHandle"/> describing the window handle, or null if the handle
         /// could not be retrieved.
         /// </returns>
-        public IPlatformHandle? TryGetPlatformHandle() => PlatformImpl?.Handle;
+	public IPlatformHandle? TryGetPlatformHandle() => ((IWindowBaseImpl?) PlatformImpl)?.Handle;
 
         /// <summary>
         /// Trys to get the platform handle for the TopLevel-derived control.