In this commit, we ensure that any topology update is forced to go via
the `handleTopologySubscriptions` handler so that client subscriptions
and updates are handled correctly and in the correct order.
This removes a bug that could result from a client missing a
notification about a channel being closed if the client is subscribed
and shortly after, `PruneGraph` is called which would notify all
subscribed clients and possibly do so before the client subscription has
actually been persisted.
0155d5d7b0