Fix typo for issue1873

(transplanted from f230b8f4a105e1014beeee7bf7276af3b24f1f25)

sale.py

@@ -1165,7 +1165,7 @@ class SaleLine(ModelSQL, ModelView):
         ignored_ids = set(
             l.id for i in line.sale.invoices_ignored for l in i.lines)
         for invoice_line in line.invoice_lines:
-            if ((invoice_lines.invoice and
+            if ((invoice_line.invoice and
                     invoice_line.invoice.state != 'cancel') or
                 invoice_line.id in ignored_ids):
                 quantity -= uom_obj.compute_qty(invoice_line.unit,