[vtkusers] Cutting UnstructuredGrid

[Hongyu Wu]

Hi,

I got a seg fault when I tried to cut a slice (using vtkCutter) from my
UnstructuredGrid using a plane with normals other (0, 0, 1). I did succeed
in cutting with the normal (0, 0, 1) only. The cell type is 
VTK_WEDGE(13). There are 3409 points in the grid. All other visualizations
are working fine.

I actually built a small UnstructuredGrid test example with 8 points and 2
Wedge cells and cutting works fine for it with all kinds of normals. I
don't know why it doesn't work for my real grid.

Does anyone happen to know something about this? Thanks.

  -- Hongyu