MINOR: quic: Wrong loss time computation in qc_packet_loss_lookup()

This part as been modified by the RFC since our first implementation.
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index bff51ac..0a1ef8e 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -1659,7 +1659,10 @@
 			LIST_APPEND(lost_pkts, &pkt->list);
 		}
 		else {
-			pktns->tx.loss_time = tick_first(pktns->tx.loss_time, loss_time_limit);
+			if (tick_isset(pktns->tx.loss_time))
+				pktns->tx.loss_time = tick_first(pktns->tx.loss_time, loss_time_limit);
+			else
+				pktns->tx.loss_time = loss_time_limit;
 		}
 	}