Fix wrapping build errors excluding non VTK classes from wrapping
This commit fixes a regression introduced in dd71b8c1
It addresses error like the following:
Error C2440 'static_cast': cannot convert from 'vtkObjectBase *' to 'vtkImagePointDataIterator *' vtkImagingKitPythonD D:\T\VTK-Release\Wrapping\Python\vtkImagePointDataIteratorPython.cxx
Edited by Jean-Christophe Fillion-Robin