BUG/MINOR: quic: fix potential null dereference

This is not a real issue because found_in_dcid can not be set if qc is
NULL.
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index 04b4bba..f486eba 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -3923,7 +3923,7 @@
 	 *
 	 * node.leaf_p is first checked to avoid unnecessary locking.
 	 */
-	if (found_in_dcid && qc->odcid_node.node.leaf_p) {
+	if (qc && found_in_dcid && qc->odcid_node.node.leaf_p) {
 		HA_RWLOCK_WRLOCK(QUIC_LOCK, &l->rx.cids_lock);
 		ebmb_delete(&qc->odcid_node);
 		HA_RWLOCK_WRUNLOCK(QUIC_LOCK, &l->rx.cids_lock);