corrected warnings when compiling with -Wall -W

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@15412 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/pen.cpp

@@ -34,6 +34,7 @@ public:
     }
     
     wxPenRefData( const wxPenRefData& data )
+        : wxObjectRefData()
     {
         m_style = data.m_style;
         m_width = data.m_width;