Try to fix channel close issue

[yorkz1994]

This related to my comment on #109 (comment).

I managed to find the real problem.
In russh/src/client/encrypted.rs:

When received channel close message, it removes the channel first from channel map, then send back channel_close message to server by Encrypted::byte function.
But in Encrypted::byte function, it checks the channel map to actually send the message, since it has been removed, the close message never got send to the server, this keeps the server channel leak.

My solution is to move remove channel in map code into Encrypted::close function.

1. If client initiate close, Encrypted::close will be invoked, close message will be sent to server and removed in local channel map, if later received server close message, as channel has been removed, no close message will be send again.

2. If server initiate close, Encrypted::close will be invoked too, close message will be sent to server and removed in local channel map.

[Eugeny]

Wow - nice find, thank you for the contribution! @all-contributors please add @yorkz1994 for code

[allcontributors]

@Eugeny

I couldn't determine any contributions to add, did you specify any contributions?
Please make sure to use valid contribution names.

I've put up a pull request to add @yorkz1994! 🎉

[yorkz1994]

@Eugeny,

Do you plan for a new release to crates.io for this fix?

[Eugeny]

Just released v0.36.1 ✌️

[yorkz1994]

Excellent!
Thanks!