MINOR: resolvers: Purge answer items when a SRV resolution triggers an error

When a SRV request trigger an error, if we decide to handle the error
because last_valid duration is expired, the answer list may be purged. All
items are considered as obsolete.

src/server.c

@@ -3293,6 +3293,8 @@ int srvrq_resolution_error_cb(struct resolv_requester *requester, int error_code
 		HA_SPIN_UNLOCK(SERVER_LOCK, &s->lock);
 	}
 
+	resolv_purge_resolution_answer_records(res);
+
 	return 1;
 }