Failing event dispatch when a client disconnects unexpectedly

[yallie]

Describe the bug
When serving multiple clients with connected events and MessageEncryption enabled, server fails to dispatch new events if one of the clients disconnects unexpectedly (network error, process crash, etc).

Originates in this discussion: #62

To Reproduce
Steps to reproduce the behavior:

• Start a server and two clients
• Connect both clients to the server and subscribe to its events
• Fire an event and get it handled on both clients
• Disconnect the first client
• Fire an event and get an error
• Note that if MessageEncryption == false, everything works seamlessly

Expected behavior

• Server should handle disconnected clients gracefully.
• Clients shouldn't depend on one another.
• Server behavior shouldn't be dependent on MessageEncryption setting.

Additional notes
The issue seems to be related to the closed RsaKeyPair safe handle.