lightningd: allow account db version 18.

If you have run recent master, upgrade will fail with:

```
Cannot migrate account database version 18
```

The final migration is:

```
	/* We used to send anchors to the wallet, but set ignored tag.  Now we send
	 * them to external. */
	{SQL("UPDATE chain_events"
	     " SET account_id = (SELECT id FROM accounts WHERE name = 'external')"
	     " WHERE account_id = (SELECT id FROM accounts WHERE name = 'wallet')"
	     " AND ignored = 1"), NULL},
```

Which is harmless (we do that upgrade ourselves on migration, but if it's done already that will have no effect).

Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

wallet/account_migration.c

@@ -385,7 +385,7 @@ void migrate_from_account_db(struct lightningd *ld, struct db *db)
 		goto out;
 	}
 	/* Last migration was 24.08.  Migrate there first if this happens. */
-	if (version != 17)
+	if (version != 17 && version != 18)
 		fatal("Cannot migrate account database version %i", version);
 	chain_events = list_chain_events(tmpctx, account_db);
 	channel_events = list_channel_events(tmpctx, account_db);