gossipd: don't ignore first update if timestamp == 0

Since we initialize last_timestamp to 0, we ignore any initial update
with this timestamp.  Don't compare it if we don't already have an
update, and don't initialize it, so valgrind can tell us if we use
it accidentally.

	b'lightning_gossipd(3368): TRACE: Received channel_update for channel 6892:2:1(0)'
	b'lightning_gossipd(3368): TRACE: Ignoring outdated update.'
	b'lightning_gossipd(3368): TRACE: Received channel_update for channel 6893:2:1(1)'
	b'lightning_gossipd(3368): TRACE: Channel 6893:2:1(1) was updated.'

The same logic applies to node_updates, so we do the same there.

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

gossipd/routing.c

@@ -77,7 +77,6 @@ struct node *new_node(struct routing_state *rstate,
 	n->out = tal_arr(n, struct node_connection *, 0);
 	n->alias = NULL;
 	n->node_announcement = NULL;
-	n->last_timestamp = 0;
 	n->addresses = tal_arr(n, struct ipaddr, 0);
 	node_map_add(rstate->nodes, n);
 	tal_add_destructor(n, destroy_node);
@@ -229,7 +228,6 @@ struct node_connection *half_add_connection(struct routing_state *rstate,
 	nc = get_or_make_connection(rstate, from, to);
 	nc->short_channel_id = *schanid;
 	nc->active = false;
-	nc->last_timestamp = 0;
 	nc->flags = flags;
 	nc->min_blocks = 0;
 	nc->proportional_fee = 0;
@@ -253,7 +251,6 @@ struct node_connection *add_connection(struct routing_state *rstate,
 	c->delay = delay;
 	c->min_blocks = min_blocks;
 	c->active = true;
-	c->last_timestamp = 0;
 	memset(&c->short_channel_id, 0, sizeof(c->short_channel_id));
 	c->flags = get_channel_direction(from, to);
 	return c;
@@ -758,7 +755,7 @@ void handle_channel_update(struct routing_state *rstate, const u8 *update, size_
 					    &short_channel_id));
 		tal_free(tmpctx);
 		return;
-	} else if (c->last_timestamp >= timestamp) {
+	} else if (c->channel_update && c->last_timestamp >= timestamp) {
 		status_trace("Ignoring outdated update.");
 		tal_free(tmpctx);
 		return;
@@ -851,7 +848,7 @@ void handle_node_announcement(
 		status_trace("Node not found, was the node_announcement preceeded by at least channel_announcement?");
 		tal_free(tmpctx);
 		return;
-	} else if (node->last_timestamp >= timestamp) {
+	} else if (node->node_announcement && node->last_timestamp >= timestamp) {
 		status_trace("Ignoring node announcement, it's outdated.");
 		tal_free(tmpctx);
 		return;