Make HasValue virtual in wxDataViewModel and have implementations use it. This addresses issue https://trac.wxwidgets.org/ticket/18724

include/wx/dataview.h

@@ -208,7 +208,7 @@ public:
     // return true if the given item has a value to display in the given
     // column: this is always true except for container items which by default
     // only show their label in the first column (but see HasContainerColumns())
-    bool HasValue(const wxDataViewItem& item, unsigned col) const
+    virtual bool HasValue(const wxDataViewItem& item, unsigned col) const
     {
         return col == 0 || !IsContainer(item) || HasContainerColumns(item);
     }