MDEV-19231: Correct an assertion

BtrBulk::finish(): On error, the B-tree can be corrupted. Only upon
successful completion, it makes sense to validate the index.

storage/innobase/btr/btr0bulk.cc

@@ -1050,7 +1050,7 @@ BtrBulk::finish(dberr_t	err)
 
 	ut_ad(!sync_check_iterate(dict_sync_check()));
 
-	ut_ad(err == DB_SUCCESS
+	ut_ad(err != DB_SUCCESS
 	      || btr_validate_index(m_index, NULL, false) == DB_SUCCESS);
 	return(err);
 }