BUG/MINOR: quic: Unchecked pointer to Handshake packet number space

It is possible that there are still Initial crypto data in flight without
Handshake crypto data in flight. This is very rare but possible.

This issue was reported by handshakeloss interop test with quic-go as client
and @chipitsine in GH #2279.

No need to backport.

src/quic_tx.c

@@ -1333,6 +1333,7 @@ int qc_dgrams_retransmit(struct quic_conn *qc)
 				if (!LIST_ISEMPTY(&hfrms))
 					hpktns->tx.pto_probe = 1;
 				qc->iel->retrans_frms = &ifrms;
+				if (qc->hel)
 					qc->hel->retrans_frms = &hfrms;
 				if (!qc_send_hdshk_pkts(qc, 1, qc->iel, qc->hel))
 					goto leave;