Fix initial handshake failure blocking retries

[The-personified-devil]

When initially establishing the connection, if the handshake packet from the client doesn't arrive the client stays registered as connecting and thus retries become impossible. Adb creates a listen socket immediately upon enabling port forwarding. Because the socket gets accepted the server attempts to establish a connection and fails because adb on it's own won't send the handshake packet when the client's not running, thus blocking retries and preventing a connection being made when the client is actually started.

[zmerp]

Thanks you so much! I will merge this as is but you uncovered a pretty big flaw in the connection design: retries will fail if the connection gets interrupted any time during handshake.