Fix "abstract error" when clicking "delete" button on data sorting dialog, caused by free'd button in its OnClick event.

source/data_sorting.dfm

@@ -76,4 +76,11 @@ object DataSortingForm: TDataSortingForm
       OnClick = btnResetClick
     end
   end
+  object timerRefresh: TTimer
+    Enabled = False
+    Interval = 100
+    OnTimer = DisplaySortingControls
+    Left = 8
+    Top = 8
+  end
 end