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/bitmap.cpp

@@ -184,7 +184,7 @@ class wxBitmapRefData: public wxObjectRefData
 {
 public:
     wxBitmapRefData();
-    ~wxBitmapRefData();
+    virtual ~wxBitmapRefData();
 
     GdkPixmap      *m_pixmap;
     GdkPixbuf      *m_pixbuf;