Fix samrai reader fails with no amr mesh
Adds a sanity check in vtkAvtSTMDFileFormatAlgorithm::ValidAMR()
before actually calling vtkAvtSTMDFileFormatAlgorithm::FillAMR()
to handle cases where the mesh does not have refinement (yet), i.e., no AUXILIARY_DATA_DOMAIN_NESTING_INFORMATION
fix paraview#19972
Edited by Feimi Yu