Bringing back support for rectilinear input.

vtkExtractCTHPart in past support a vtkRectilinearGrid as input. Commit 323ad383
resulted in that ability being lost. Fixed that. Also fixing the defaults for
the newly added filter parameters to match the old version.

Change-Id: Ie163572ea34d89564feff57f40f4e58c099a0100
Merge topic 'fix_cth_part_test' into master

558b34a1 Bringing back support for rectilinear input.
Fixed bug where an empty vector was being accessed.

The code did not properly check if a vector (idMaps) was empty
before accessing it. Fixed.

Change-Id: Id8724b2f8c47ddbb5e8178523c5b7d72c9eb4914
Merge topic 'fix-smp-contour-bug' into master

16929d48 Fixed bug where an empty vector was being accessed.