Handle REQUEST_DATA_NOT_GENERATED in vtkSMPContourGrid.
When running without any contours requested and using a composite dataset as input, the pipeline currently prints a warning:
ERROR: VTK/src/Common/DataModel/vtkDataObjectTree.cxx, line 297 vtkMultiBlockDataSet (0x3f3e440): Structure does not match. You must use CopyStructure before calling this method.
Handling this request prevents the composite dataset structure from being reset.