Fix axis clipping crash + fix Initialize for HTG
Clipping crash filter was crashing due to inexact Dimensionsattribute
in the filter. An other crash happened when clipping multiple times an
HTG with the same filter and different parameters. Crash was due to an
incomplete Initialize method in vtkHyperTreeGrid, causing its Mask
attribute to share the same address as OutMask attribute in
vtkHyperTreeGridAxisClipFilter, messing up the algorithm.
vtkHyperTreeGrid::Initialize has been completed with initializing all
other miscellaneous attributes.
Edited by Yohann Bearzi (Kitware)