[vtkusers] There is problem with the vtkCellArray's GetNextCell function

[Dhaniram Kshirsagar]

Hi vtkDevs,

There is problem with the use of GetNextCell member of vtkCellArray.

That is once you use this then with this same fuction you will not be
able to get the cells again. I think there might be some restore
problem with pointer to cell array.

Please let me know if it is a implemetion or bug.

Thanks
Dhani