vtkOpenGLPolyDataMapper crashes on empty cell scalars array
When I supply a vtkPolyData with an empty cell scalars array (which is an error in itself of course) as in the attached script crash_on_empty_cell_scalars.py, vtkOpenGLPolyDataMapper crashes in vtkOpenGLPolyDataMapper::AppendCellTextures (vtk8.1.0).
As a minor side note: https://github.com/Kitware/VTK/blob/9884dbfc018ae2695d0ea539479878bccefb69a9/Rendering/OpenGL2/vtkOpenGLPolyDataMapper.cxx#L2635 declares an unused tmpColors vector.