Add wxDataViewCtrl::GetSortingColumn() stubs

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@48654 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/dataview.cpp

@@ -1256,6 +1256,7 @@ void wxDataViewRenderer::SetMode( wxDataViewCellMode mode )
         break;
     }
 
+    // This value is most often ignored in GtkTreeView    
     GValue gvalue = { 0, };
     g_value_init( &gvalue, gtk_cell_renderer_mode_get_type() );
     g_value_set_enum( &gvalue, gtkMode );
@@ -3111,6 +3112,11 @@ bool wxDataViewCtrl::ClearColumns()
     return true;
 }
 
+wxDataViewColumn *wxDataViewCtrl::GetSortingColumn() const
+{
+    return NULL;
+}
+
 void wxDataViewCtrl::Expand( const wxDataViewItem & item )
 {
     GtkTreeIter iter;