Fix the window that flashed by (#254)

Author: ChenYiLins

src/WinUIEx/TrayIcon.cs

@@ -180,9 +180,9 @@ private void ShowFlyout(FlyoutBase flyout)
             _currentFlyout = flyout;
             var grid = ((Microsoft.UI.Xaml.Controls.Grid)_window.Content);
             grid.ContextFlyout = flyout;
+            _window.AppWindow.MoveAndResize(new Windows.Graphics.RectInt32(location.X, location.Y, 0, 0), Microsoft.UI.Windowing.DisplayArea.GetFromPoint(new Windows.Graphics.PointInt32(0, 0), Microsoft.UI.Windowing.DisplayAreaFallback.Primary));
             _window.Activate();
             _window.Show();
-            _window.AppWindow.MoveAndResize(new Windows.Graphics.RectInt32(location.X, location.Y, 0, 0), Microsoft.UI.Windowing.DisplayArea.GetFromPoint(new Windows.Graphics.PointInt32(0, 0), Microsoft.UI.Windowing.DisplayAreaFallback.Primary));
             WindowExtensions.SetForegroundWindow(_window);
             double w = (location.Width - location.X) /  grid.XamlRoot.RasterizationScale;
             double h = (location.Height - location.Y) / grid.XamlRoot.RasterizationScale;