client: Discard proxies with no implementation at dispatch time

client: Discard proxies with no implementation at dispatch time

We need to queue up events even if a proxy doesn't have an implementation
(listener).  In case of server created new objects, the client haven't
had a chance to set the listener when the first events to the new object
come in.  So now we always queue up events and discard them at
dispatch time if they don't have a listener at that point.