close socket properly during session init when connection is not exist anymore

[icehess]

We observed when a connection is opened and closed in a short amount of time before even gen_smtp_server_session is started, the call to socket:peername/1 causes crash in gen_smtp_server_session and the socket remains open.

If this kind of connections happen periodically (e.g. during a Haproxy health check) , the node eventually would run out of file descriptors.

This tries to handle the call to socket:peername/1 and will close the socket if the connection is closed during initializing of a session.

[mworrell]

The 'andalso' suggests a boolean check, I would prefer to have the PeerName check and the init return handled separately. In this case you can have an init_peername({error, _}, ...) that closes the socket and a init_peername({ok, ...}, ...) that handles the init.

[mworrell]

Merging anyway, as the change is important enough and works well.