lightningd: add comment on why we have "useless" initialization.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/peer_control.c

@@ -901,6 +901,7 @@ static struct command_result *json_close(struct command *cmd,
 {
 	const jsmntok_t *idtok;
 	struct peer *peer;
+	/* FIXME: gcc 7.3.0 thinks this might not be initialized. */
 	struct channel *channel = NULL;
 	unsigned int *timeout;
 	bool *force;