mark all dtors which are virtual because base class dtor is virtual explicitly virtual themselves

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41020 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/colour.cpp

@@ -35,7 +35,7 @@ public:
         m_colormap = NULL;
     }
 
-    ~wxColourRefData()
+    virtual ~wxColourRefData()
     {
         FreeColour();
     }