Fix memory leak when wxDataViewCtrl is deleted (wxGTK)

Need to delete wxGtkTreeModelNode structure

src/gtk/dataview.cpp

@@ -3544,6 +3544,7 @@ wxDataViewCtrlInternal::~wxDataViewCtrlInternal()
 
     g_object_unref( m_gtk_model );
 
+    delete m_root;
     delete m_dragDataObject;
     delete m_dropDataObject;
 }