lightningd/peer_control: initialize error pointer in handle_peer_spoke

The local variable `error` in handle_peer_spoke() is declared as a
pointer type with no initialization. Several error paths jump to the
`send_error` label where `error` is dereferenced (passed to
tal_hex() and towire_connectd_peer_send_msg()). While sockpair()
currently sets the `error` pointer via the output parameter on
failure, the declaration should be initialized to NULL as a defensive
measure and to avoid undefined behavior if code paths change.

Fixes #8849

Changelog-Fixed: peer_control: initialize error pointer in handle_peer_spoke to NULL to prevent undefined behavior on error paths.

Author: Storm Knight

lightningd/peer_control.c

@@ -2017,7 +2017,7 @@ void handle_peer_spoke(struct lightningd *ld, const u8 *msg)
 	struct channel_id channel_id;
 	struct peer *peer;
 	bool dual_fund;
-	const u8 *error;
+	const u8 *error = NULL;
 	int other_fd;
 	struct peer_fd *pfd;
 	char *errmsg;