Prevent vtkCutter to access invalid object in RequestData

In case of multi-block that contains vtkTable, the vtkCutter is
not supposed to process anything and therefore should make sure
only valid data can be processed.

Add a check to prevent invalid object access.

Change-Id: If9d87e99c7ded9ba9b56acc54d1eabe319517498
Merge topic '14000-multi-block-table-cut' into master

c43f706b Prevent vtkCutter to access invalid object in RequestData