Billing: fix calculation

Elwig/Documents/CreditNote.cs

@@ -34,7 +34,7 @@ namespace Elwig.Documents {
                 FROM v_delivery v
                 JOIN delivery_part p ON (p.year, p.did, p.dpnr) = (v.year, v.did, v.dpnr)
                 WHERE (v.year, v.mgnr) = ({c.Year}, {c.Member.MgNr})
-                ORDER BY sortid, LENGTH(attributes) DESC, attributes, kmw DESC, date, time, dpnr
+                ORDER BY sortid, attribute_prio DESC, COALESCE(attrid, '~'), kmw DESC, date, time, dpnr
                 """).ToList();
         }
     }}