avoid NULL casts, clang says casting nullptr_t is not allowed

closes #15660


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75162 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/datavcmn.cpp

@@ -1801,7 +1801,7 @@ void wxDataViewListStore::SetItemData( const wxDataViewItem& item, wxUIntPtr dat
 wxUIntPtr wxDataViewListStore::GetItemData( const wxDataViewItem& item ) const
 {
     wxDataViewListStoreLine* line = m_data[GetRow(item)];
-    if (!line) return static_cast<wxUIntPtr>(NULL);
+    if (!line) return 0;
 
     return line->GetData();
 }