Windows: AFSCleanup move CCb access inside try block

A crash dump was examined which showed a deadlock due to the leak
of a SectionObjectResource in a code path in which the holding thread
could not have obtained it.  The FileObject->FsContext2 (Ccb) pointer
referred to invalid memory which may have been due to pool corruption.
The only code path in which the SectionObjectResource is held exclusive
and then the Ccb pointer is used outside of a try-except block is in
AFSCleanup().  Move this reference inside the try-except block just in
case.  If the Ccb is invalid, at least this way AFSRedirLib will catch
the exception and free the SectionObjectResource before continuing.

Reviewed-on: http://gerrit.openafs.org/9892
Reviewed-by: Peter Scott <pscott@kerneldrivers.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit c42912d6da6ff7536b1301b4fb7f556513e8692c)

Change-Id: I20ba146da60cd30721653ed6abb65802457352ea
Reviewed-on: http://gerrit.openafs.org/9897
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>