Billing: Create credit notes only for members who receive a payment

Elwig/Helpers/Billing/BillingVariant.cs

@@ -80,7 +80,7 @@ namespace Elwig.Helpers.Billing {
                         LEFT JOIN v_penalty_area_commitments u ON (u.year, u.mgnr) = (s.year, m.mgnr)
                         LEFT JOIN v_auto_business_shares a ON (a.year, a.mgnr) = (s.year, m.mgnr)
                         LEFT JOIN payment_custom x ON (x.year, x.mgnr) = (s.year, m.mgnr)
-                    WHERE s.year = {Year} AND v.avnr = {AvNr};
+                    WHERE s.year = {Year} AND v.avnr = {AvNr} AND p.amount > COALESCE(lp.amount, 0);
                     """);
             await cnx.ExecuteBatch($"""
                 UPDATE payment_variant SET test_variant = FALSE WHERE (year, avnr) = ({Year}, {AvNr});