sieve: improve address tests

* libmu_sieve/tests.c (retrieve_address): Treat MU_ERR_EMPTY_ADDRESS
as MU_ERR_NOENT.  This complements 678d9367

@@ -71,9 +71,16 @@ retrieve_address (void *item, void *data, size_t idx, char **pval)
 	return MU_ERR_NOENT;
       rc = mu_address_create (&ap->addr, val);
       free (val);
-      if (rc)
+      switch (rc)
+	{
+	case MU_ERR_EMPTY_ADDRESS:
+	case MU_ERR_NOENT:
+	  return MU_ERR_NOENT;
+
+	default:
 	  return rc;
 	}
+    }
 
   rc = ap->aget (ap->addr, idx+1, pval);
   if (rc)