RegionSizeof contains several integer overflows if a large length
value is passed in.  Once we fix it to return 0 on overflow, we
also have to fix the callers to handle this error condition

v2: Fixed limit calculation in RegionSizeof as pointed out by jcristau.
v3: backport to nx-libs 3.6.x (Mike DePaulo)
Reported-by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Julien Cristau <jcristau@debian.org>

Conflicts:
	dix/region.c
	include/regionstr.h