Merge branch '1650-fix-race-in-killoldestclient-v9_16' into 'v9_16'

Destroy query in killoldestquery under a lock.

See merge request !3162

lib/ns/client.c

@@ -170,13 +170,11 @@ ns_client_killoldestquery(ns_client_t *client) {
 	oldest = ISC_LIST_HEAD(client->manager->recursing);
 	if (oldest != NULL) {
 		ISC_LIST_UNLINK(client->manager->recursing, oldest, rlink);
-		UNLOCK(&client->manager->reclock);
 		ns_query_cancel(oldest);
 		ns_stats_increment(client->sctx->nsstats,
 				   ns_statscounter_reclimitdropped);
-	} else {
-		UNLOCK(&client->manager->reclock);
 	}
+	UNLOCK(&client->manager->reclock);
 }
 
 void