When trying to process file paths the tokens %H, %L, & %S are expanded
to $HOME, the standard compose file path & the xlocaledir path.
If enough of these tokens are repeated and values like $HOME are set to
very large values, the calculation of the total string size required to
hold the expanded path can overflow, resulting in allocating a smaller
string than the amount of data we'll write to it.

Simply restrict all of these values, and the total path size to PATH_MAX,
because really, that's all you should need for a filename path.
Reported-by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Matthieu Herrb <matthieu.herrb@laas.fr>
Signed-off-by: Julien Cristau <jcristau@debian.org>
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>