Fix post_msg implementation bug

[grandnew]

I think the error handling code of post_msg is wrongly implemented due to coding typo. The EPIPE should be also considered and then return -1, just like PPTP_write:

accel-ppp/accel-pppd/ctrl/pptp/pptp.c

Lines 539 to 570 in 1b8711c

	static int pptp_write(struct triton_md_handler_t *h)
	{
	struct pptp_conn_t *conn = container_of(h, typeof(*conn), hnd);
	int n;
	while (1) {
	n = write(h->fd, conn->out_buf+conn->out_pos, conn->out_size-conn->out_pos);
	if (n < 0) {
	if (errno == EINTR)
	continue;
	if (errno == EAGAIN)
	n = 0;
	else {
	if (errno != EPIPE) {
	if (conf_verbose)
	log_ppp_info2("pptp: post_msg: %s\n", strerror(errno));
	}
	disconnect(conn);
	return 1;
	}
	}
	conn->out_pos += n;
	if (conn->out_pos == conn->out_size) {
	conn->out_pos = 0;
	conn->out_size = 0;
	triton_md_disable_handler(h, MD_MODE_WRITE);
	return 0;
	}
	}
	}

This pr fixes #158.

[Neustradamus]

Dear @grandnew,

Can you open a PR at "good" place:

• https://github.com/accel-ppp/accel-ppp

Thanks in advance.

[grandnew]

@Neustradamus Sure. Please check: accel-ppp/accel-ppp#216