silence warning about converting NULL to wxUIntPtr

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71616 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/datavcmn.cpp

@@ -1777,7 +1777,7 @@ void wxDataViewListStore::SetItemData( const wxDataViewItem& item, wxUIntPtr dat
 wxUIntPtr wxDataViewListStore::GetItemData( const wxDataViewItem& item ) const
 {
     wxDataViewListStoreLine* line = m_data[wxPtrToUInt( item.GetID() ) - 1];
-    if (!line) return NULL;
+    if (!line) return static_cast<wxUIntPtr>(NULL);
 
     return line->GetData();
 }