LWP: don't copy pid to a null pointer

In LWP_CreateProcess we take a pid. if it's null, don't crash.

Reviewed-on: http://gerrit.openafs.org/3556
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 5d218831f3186d0d1dc7d3b00dd4a3b6a4a8757c)

Change-Id: I96c0e2a8858fa929f0de22a774050aa63a200101
Reviewed-on: http://gerrit.openafs.org/9414
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>