Fully disconnect when remote server ends connection.

[invariablyafk]

When the remote server ends the connection, the message (disconnected by server) is presented, but ssheven is not in a state that is ready to start a new connection. This change prevents the user from having to select File>Disconnect before selecting File>Connect.. for a new session.

[cy384]

thanks for the fix, I'll get it merged once I have a chance to test it!

[invariablyafk]

Sounds great. Thanks for the app. It is the best one I've used on classic Macs to date.

[cooljeanius]

(whitespace could probably be neatened a bit, but that's pretty minor and shouldn't block merging; @cy384 can always clean it up later after merging...)