Ensure that the given strings length in an XkbSetGeometry request remain
within the limits of the size of the request.

v3: backport to nx-libs 3.6.x because this is
the CVE-2015-0255 fix (Mike DePaulo)
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit 20079c36cf7d377938ca5478447d8b9045cb7d43)
(cherry picked from commit f160e722672dbb2b5215870b47bcc51461d96ff1)
Signed-off-by: Julien Cristau <jcristau@debian.org>