libadmin: Don't pass garbage to pts_GroupCreate

The libadmin pts_GroupCreate function uses the value passed to
it in newGroupId to control whether the group is being created
with a user supplied ID or not.

Initialise this value in the caller, so we don't end up creating
groups with corrupt ids.

Caught by clang (#985978)

Reviewed-on: http://gerrit.openafs.org/9400
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit ece7bd669af0c58dcaa2589e093387adb7d1756a)

Change-Id: I51750db47f7709406c079c4fbeec561228359e73
Reviewed-on: http://gerrit.openafs.org/11049
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>