do not display the checkered keyboard focus rectangle around the DialogHost when the user happens to dismiss a dialog popup using a keyboard gesture (#2265)

Author: BigBadBleuCheese

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.DialogHost.xaml

@@ -13,6 +13,7 @@
     </Style>
 
     <Style TargetType="{x:Type wpf:DialogHost}">
+        <Setter Property="FocusVisualStyle" Value="{x:Null}" />
         <Setter Property="DialogMargin" Value="35" />
         <Setter Property="wpf:ShadowAssist.ShadowDepth" Value="Depth5" />
         <Setter Property="DialogTheme" Value="Inherit" />