fix: property grid can not show whole content issue.

src/Shared/HandyControl_Shared/Controls/PropertyGrid/PropertyItemsControl.cs

@@ -11,6 +11,8 @@ public class PropertyItemsControl : ListBox
 #if !NET40
         VirtualizingPanel.SetIsVirtualizingWhenGrouping(this, true);
         VirtualizingPanel.SetScrollUnit(this, ScrollUnit.Pixel);
+#else
+        System.Windows.Controls.ScrollViewer.SetCanContentScroll(this, false);
 #endif
     }
 }