Bug0014435 Fix hyperstreamline segfault when no cell scalars.

per http://www.vtk.org/Bug/view.php?id=14435

Thanks Raine for the patch.

Change-Id: I5b5bd31e630fc6faf5576a9af4459b681e366145
Merge topic '0014435-make-hyperstreamline-handle-no-scalars' into master

9ec53a31 Bug0014435 Fix hyperstreamline segfault when no cell scalars.