message: Fix for VTK6 build
diff: #pragma clang diagnostic ignored "-Winconsistent-missing-destructor-override"
  // vtk
  +#include <vtkSmartPointer.h>
  #include <vtkCell.h>
  #include <vtkCellData.h>
  #include <vtkCellTypes.h>
  @@ -108,7 +109,8 @@ namespace ospray {
  if (pd) {
  for (int i = 0; i < pd->GetNumberOfArrays(); i++) {
  vtkAbstractArray *ad = pd->GetAbstractArray(i);
  - int nDataPoints = ad->GetNumberOfValues();
  + int nDataPoints = ad->GetNumberOfTuples()
  + * ad->GetNumberOfComponents();
  auto array = make_vtkSP(vtkDataArray::SafeDownCast(ad));
  