message: Handle special case where B_offd is empty
diff: @@ -1520,10 +1520,14 @@ hypre_ParCSRMatrixSum(hypre_ParCSRMatrix *A,
  hypre_CSRMatrix *A_offd = hypre_ParCSRMatrixOffd(A);
  hypre_CSRMatrix *B_diag = hypre_ParCSRMatrixDiag(B);
  hypre_CSRMatrix *B_offd = hypre_ParCSRMatrixOffd(B);
  + HYPRE_Int ncols_B_offd = hypre_CSRMatrixNumCols(B_offd);
  HYPRE_Int error;
  error = hypre_CSRMatrixSum(A_diag, beta, B_diag);
  + if (ncols_B_offd > 0) /* treat B_offd as zero if it has no columns */
  + {
  error = error ? error : hypre_CSRMatrixSum(A_offd, beta, B_offd);
  + }
  return error;
  }
  