message: prevent Convert_Array_IS from segfaulting
diff: @@ -4185,8 +4185,8 @@ static PetscErrorCode Convert_Array_IS(MPI_Comm comm, bool islist,
  const mfem::Array<int> *list,
  PetscInt st, IS* is)
  {
  - PetscInt n = list->Size(),*idxs;
  - const int *data = list->GetData();
  + PetscInt n = list ? list->Size() : 0,*idxs;
  + const int *data = list ? list->GetData() : NULL;
  PetscErrorCode ierr;
  PetscFunctionBeginUser;
  