fix a race condition

Setting `closed` on the socket (which can mean either "the socket is broken"
or "we should close the socket at the next opportunity") was racing against
the final write. Even if socket.closed is true, we should attempt to send
buffered message data to the socket, before we send the `finalData` and
actually call `Close`.

irc/socket.go

@@ -254,7 +254,7 @@ func (socket *Socket) performWrite() (closed bool) {
 	socket.Unlock()
 
 	var err error
-	if !closed && len(buffers) > 0 {
+	if 0 < len(buffers) {
 		// on Linux, the runtime will optimize this into a single writev(2) call:
 		_, err = (*net.Buffers)(&buffers).WriteTo(socket.conn)
 	}