channeld: fail channel on zero next_commitment_number

The existing BOLT #2 quote already required this, but the first
bullet was unimplemented: the only zero check sat under
next_commitment_number == next_index[REMOTE] - 1, after the
stale-revocation warning.

Implement that bullet next to the quote, and drop the nested copy.

Fixes: #9425
Changelog-Fixed: Protocol: immediately fail the channel if channel_reestablish next_commitment_number is zero.
Reported-by: Leo Nash (@tankyleo)
Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

Author: vincenzopalazzo

channeld/channeld.c

@@ -5990,6 +5990,11 @@ static void peer_reconnect(struct peer *peer,
 	 *    - MUST NOT retransmit `channel_ready`, but MAY send `channel_ready` with
 	 *      a different `short_channel_id` `alias` field.
 	 */
+	if (next_commitment_number == 0)
+		peer_failed_err(peer->pps,
+				&peer->channel_id,
+				"bad reestablish commitment_number: %"PRIu64,
+				next_commitment_number);
 
 	if (peer->channel_ready[LOCAL]
 	    && peer->next_index[LOCAL] == 1
@@ -6102,14 +6107,6 @@ static void peer_reconnect(struct peer *peer,
 	 *       `commitment_signed`.
 	 */
 	if (next_commitment_number == peer->next_index[REMOTE] - 1) {
-		/* We completed opening, we don't re-transmit that one! */
-		if (next_commitment_number == 0)
-			peer_failed_err(peer->pps,
-					 &peer->channel_id,
-					 "bad reestablish commitment_number: %"
-					 PRIu64,
-					 next_commitment_number);
-
 		if (!recv_tlvs || !recv_tlvs->next_funding)
 			retransmit_commitment_signed = true;
 		else