Windows: Fix out of range pointer validation

The ACL, Stat, and Volume pointer validation checks did not take
into account that NULL is a valid pointer value.  As a result the
cache validation failed.

Change-Id: I538310d534fd4ada383d5bf0dc58d49206fe3dfb
Reviewed-on: http://gerrit.openafs.org/10453
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: cm_FindVolumeByFID

cm_GetVolumeByFID() does not query the vldb if the volume group
is not known to the cache manager.   cm_FindVolumeByFID() is to
be used in cases where the volume group data must be known for the
operation to successfully complete.

Change-Id: I9bb3bd13f14dea534952495b00a3348aafd2d591
Reviewed-on: http://gerrit.openafs.org/10465
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>