Windows: Fix caching of non-existing vols

Windows: Fix caching of non-existing vols

In cm_UpdateVolumeLocation() the conditional that would
trigger the immediate return of CM_ERROR_NOSUCHVOLUME
was backwards which prevented the caching from working.

cm_CheckOfflineVolumes() is called by the daemon thread
to reset the status of offline volumes.  Non-existing
volumes are by definition offline and cannot be brought
online.  Therefore, the cm_CheckOfflineVolumes() function
should skip volumes with the CM_VOLUMEFLAG_NOEXIST flag
set.

Change-Id: I65534b78842b4887d2fde67162a9d854437001ed
Reviewed-on: http://gerrit.openafs.org/4597
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-on: http://gerrit.openafs.org/4598
Reviewed-by: Derrick Brashear <shadow@dementia.org>