BOLT 7: note use of 0 timestamp/checksum if channel_update in that di…

…r not received.

We can have channels which haven't been updated in both directions (if neither, we
should not be including them at all).

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

07-routing-gossip.md

@@ -697,10 +697,10 @@ Currently, the only valid `option_extended_query_flag` is 1. The corresponding `
   * [`4`:`timestamp_node_id_2`]
   * [`4`:`checksum_node_id_2`]
 
-* `timestamp_node_id_1` is the timestamp of the `channel_update` for `node_id_1`
-* `checksum_node_id_1` is the checksum of the `channel_update` for `node_id_1`
-* `timestamp_node_id_2` is the timestamp of the `channel_update` for `node_id_2`
-* `checksum_node_id_1` is the checksum of the `channel_update` for `node_id_2`
+* `timestamp_node_id_1` is the timestamp of the `channel_update` for `node_id_1`, or 0 if there was no `channel_update` from that node.
+* `checksum_node_id_1` is the checksum of the `channel_update` for `node_id_1`, or 0 if there was no `channel_update` from that node.
+* `timestamp_node_id_2` is the timestamp of the `channel_update` for `node_id_2`, or 0 if there was no `channel_update` from that node.
+* `checksum_node_id_1` is the checksum of the `channel_update` for `node_id_2`, or 0 if there was no `channel_update` from that node.
 
 The checksum of a `channel_update` is the Adler32 checksum of this `channel_update` without its `signature` and `timestamp` fields.