Reset the io_error_fd right before the generator kills off the receiver

(because the death of the receiver will close the fd and cause the
generator to fail in any subsequent IO).

main.c

@@ -461,6 +461,7 @@ static int do_recv(int f_in,int f_out,struct file_list *flist,char *local_name)
 	}
 	io_flush();
 
+	io_set_error_fd(-1);
 	kill(pid, SIGUSR2);
 	wait_process(pid, &status);
 	return status;