BUG: Crash in PrintSelf

vtkTreeDifferenceFilter crashed on some platforms in PrintSelf. If
IdArrayName, ComparisionArrayName or OutputArrayName were null,
PrintSelf crashed on some platforms.

Change-Id: Iacba9dc5b9c355115a9eec3df875fa0a55f3903a
Merge topic 'TreeDifferenceFilterDefect' into master

27f95b9a BUG: Crash in PrintSelf