Fixed merge product button

prs.desktop/Panels/Products/Locations/StockTakeWindow.xaml.cs

@@ -500,8 +500,7 @@ namespace PRSDesktop
     }
 
     #region Intermediate Class
-    [DoNotPersist]
-    public class StockTakeHolding : Entity
+    public class StockTakeHolding : BaseObject
     {
         [DoubleEditor(Editable = Editable.Disabled)]
         public double OriginalQty { get; set; }