Fix file transfers failing at 99% over IRC
File transfers over IRC sometimes failed because the sender close()d the socket before reading everything from it, resulting in a TCP RST packet being sent, which was interpreted by the receiver as a problem with the connection, sometimes dropping the last few bytes of the file as a result.

This patch reads everything from the socket before closing, thus avoiding the RST packet issue.

Tested on Windows, Linux, Windows-to-Linux and vice-versa IRC file transfers.