using SSH: the output from the program (file transfer driver, door game)
would reach the SSH client, but input from the client (or user) would not
reach the external program:
passthru_output_thread() - responsible for SSH input from the client/user
to be sent to a "raw" pass-through socket used by the external program,
had a reversed logic bug added around rev 1.686.
Problem was introduced as part of the cryptlib update/SSH overhaul of
early 2018. Thanks to Thumper @ THEWASTE for the bug report!