Fix cross_bound to not return 1 for zero-length regions.  Fixes regression
when sending null ISO packets.
Signed-off-by: NJody McIntyre <scjody@steamballoon.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>