Fixed wrongful logic for ExtractOnlyBoundaryCells in vtkExtractGeometry.

The ExtractOnlyBoundaryCells is not working properly due to some logic
errors in deciding when to extract cells if both ExtractBoundaryCells
and ExtractOnlyBoundaryCells are on. Fixed it.

Change-Id: I0574c672507ca610b1e77272d12f4e8acc3efa0c
Merge topic 'extract-boundaryonly-bug' into master

3299c70d Fixed wrongful logic for ExtractOnlyBoundaryCells in vtkExtractGeometry.