On Windows, also call shutdown() while closing the client socket.
Further experimentation shows that commit
6051857fc is not sufficient
when using (some versions of?) OpenSSL. The reason is obscure, but
calling shutdown(socket, SD_SEND) improves matters.
Per testing by Andrew Dunstan and Alexander Lakhin.
Back-patch as before.
Discussion: https://postgr.es/m/
af5e0bf3-6a61-bb97-6cba-
061ddf22ff6b@dunslane.net