There's two situations where we're missing info.
One is we get a 'channel_closed' event (but there's no 'channel_open')
The other is a balance_snapshot arrives with information about accounts
that doesn't match what's already on disk. (For some of these cases, we
may be missing 'channel_open' events..)
In the easy case (no channel_open missing), we just figure out what the
When the node starts up, it records missing/updated account balances
to the 'channel' events... which is kinda fucked for wallet + external
events now that i think about it but these are all treated the same
anyway so it's fine.
This is the magic piece that lets your bookkeeping data startup ok on an
already running/established node.
