MINOR: quic: Add TX packets at the very last time to their tree.

If we add TX packets to their trees before sending them, they may
be detected as lost before being sent. This may make haproxy crash
when it retreives the prepared packets from TX ring buffers, dereferencing
them after they have been freed.
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index 8340be6..5bc3495 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -2221,6 +2221,7 @@
 				qc_set_timer(ctx);
 			TRACE_PROTO("sent pkt", QUIC_EV_CONN_SPPKTS, ctx->conn, pkt);
 			next_pkt = pkt->next;
+			eb64_insert(&pkt->pktns->tx.pkts, &pkt->pn_node);
 			quic_tx_packet_refdec(pkt);
 		}
 	}
@@ -3931,7 +3932,6 @@
 		qc->path->prep_in_flight += pkt->len;
 	}
 	pkt->pktns = qel->pktns;
-	eb64_insert(&qel->pktns->tx.pkts, &pkt->pn_node);
 	TRACE_LEAVE(QUIC_EV_CONN_HPKT, qc->conn, pkt);
 
 	return pkt;
@@ -4132,7 +4132,6 @@
 		qc->path->prep_in_flight += pkt->len;
 	}
 	pkt->pktns = qel->pktns;
-	eb64_insert(&qel->pktns->tx.pkts, &pkt->pn_node);
 	TRACE_LEAVE(QUIC_EV_CONN_PAPKT, qc->conn, pkt);
 
 	return pkt;