bluetooth: mesh: pb_adv: check SegN in Transaction Continuation PDU

Check that SegN is not 0. SegN = 0 is invalid as the first segment is
sent in Transaction Start PDU.

Signed-off-by: Pavel Vasilyev <[email protected]>
(cherry picked from commit 427cf0d)

Author: PavelVPV

subsys/bluetooth/mesh/pb_adv.c

@@ -515,7 +515,7 @@ static void gen_prov_cont(struct prov_rx *rx, struct net_buf_simple *buf)
 		return;
 	}
 
-	if (seg > link.rx.last_seg) {
+	if (seg > link.rx.last_seg || seg == 0) {
 		LOG_ERR("Invalid segment index %u", seg);
 		prov_failed(PROV_ERR_NVAL_FMT);
 		return;