[new-owner-report] modify report row->value accessor

Previously each owner-table row's value would access split's
amount. But this fails for payments spanning multiple invoices,
because these (with a single split to bank) will have a split for each
invoice. Hence split->amount gets only 1 invoice payment amount.

This change modifies to obtain the sum total of split->amounts in the
APAR account thus handles multi-invoice payments correctly.

gnucash/report/business-reports/new-owner-report.scm

@@ -447,7 +447,7 @@
       (let* ((split (car splits))
              (txn (xaccSplitGetParent split))
              (date (xaccTransGetDate txn))
-             (value (xaccSplitGetAmount split))
+             (value (xaccTransGetAccountValue txn acc))
              (value (if payable? (- value) value))
              (invoice (gncInvoiceGetInvoiceFromTxn txn))
              (invoice-splits