race condition:
- a client is closed at the same time as an incoming SUB message occurs.
- the subscription is added to the srv.sl even though the socket is
closed.
- the connection cleanup has already run, so the bad state is never
corrected
- now messages may be forwarded to a client without a connection
- messages will not be forwarded to a router that needs it now, because
processMsg assumes the router already received it
