Windows: FindObjectInfo refcnt under lock

AFSFindObjectInfo performed the search of Volume object tree protected by
the TreeLock but dropped the lock before incrementing the reference count.
This behavior contributed to a race with the AFSPrimaryVolumeWorkerThread
which has to drop the VolumeCB TreeLock periodically in order to safely
cleanup FCBs.

Change-Id: I0cba4a118e4835edee7702db97846567618e0adf
Reviewed-on: http://gerrit.openafs.org/9719
Reviewed-by: Peter Scott <pscott@kerneldrivers.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>