If the loss detection timer has fired we may not have lost packets

We calculate the delay from the point that a packet arrives until it will
be counted as lost based on rtt info. Looking at all the packets we can
then calculate the earliest time that a packet will be counted as lost.
When that timer fires the latest rtt info may have changed and therefore
the packet may no longer be counted as lost yet.

We should not assume that just because the ackm timeout has fired that
there will definitely be lost packets.

Fixes #22538

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from #22541)

ssl/quic/quic_ackm.c

@@ -1301,8 +1301,8 @@ int ossl_ackm_on_timeout(OSSL_ACKM *ackm)
     if (!ossl_time_is_zero(earliest_loss_time)) {
         /* Time threshold loss detection. */
         lost_pkts = ackm_detect_and_remove_lost_pkts(ackm, pkt_space);
-        assert(lost_pkts != NULL);
-        ackm_on_pkts_lost(ackm, pkt_space, lost_pkts, /*pseudo=*/0);
+        if (lost_pkts != NULL)
+            ackm_on_pkts_lost(ackm, pkt_space, lost_pkts, /*pseudo=*/0);
         ackm_set_loss_detection_timer(ackm);
         return 1;
     }