Fix crash when extracting selections from multiblock data sets with varied vtkDataObject leaves

There were some crashes encountered when extracting a selection in a vtkMultiBlockDataSet (paraview/paraview!18299). The main issue was that vtkDataObjects might not have a particular field attribute (e.g. point data, cell data, row data), and we were not handling that properly. Fixed crashes and added a test to exercise selections on a "diverse" multiblock dataset.