tty: Don't forget to add eol when inverting slave pts paths

Otherwise next strcat get confused

 | (00.024843)     26: Error (files-reg.c:1528): Can't open file dev/pts/g:��^?ptmx on restore: No such file or directory
 | (00.024846)     26: Error (files-reg.c:1470): Can't open file dev/pts/g:��^?ptmx: No such file or directory
 | (00.024849)     26: Error (tty.c:545): tty: Can't open dev/pts/g:��^?ptmx: No such file or directory

Reported-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@virtuozzo.com>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Tested-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>