Bug 797521 - Receivable Aging (beta): include earliest split

When processing invoice->payments, we used gnc-lot-get-earliest-split
to find the lot opening-split to skip it.

However it does not always return the lot opening-split, because a
lot-reducing split may be dated earlier than the lot opening-split.

This change means that the posting-split is processed together with
the payment splits, but its PaymentAcctSplitList is null, so it does
not add any row to the result.

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

@@ -309,8 +309,7 @@
 
   (define (make-invoice->payments-table invoice)
     (define lot (gncInvoiceGetPostedLot invoice))
-    (let lp ((invoice-splits (delete (gnc-lot-get-earliest-split lot)
-                                     (gnc-lot-get-split-list lot)))
+    (let lp ((invoice-splits (gnc-lot-get-split-list lot))
              (result '()))
       (match invoice-splits
         ;; finished. test for underpayment and add outstanding balance