Newly introduced widgets must be clear()-ed

Change-Id: Ibae1aa4fc8df3f5b0a2448cca27f129993eea86f

svx/source/sidebar/line/LinePropertyPanel.cxx

@@ -218,6 +218,9 @@ void LinePropertyPanel::dispose()
     mpLBEdgeStyle.clear();
     mpFTCapStyle.clear();
     mpLBCapStyle.clear();
+    mpGridLineProps.clear();
+    mpBoxArrowProps.clear();
+
 
     maLineWidthPopup.dispose();
     maStyleControl.dispose();