Windows: Do not execute tasks on deleted files

Windows: Do not execute tasks on deleted files

If a cm_BkgDaemon thread finds a queued request whose cm_scache_t
has the CM_SCACHEFLAG_DELETED flag set, do not execute the request
and fail it immediately with CM_ERROR_BADFD.  Any attempt to execute
the request will fail with VNOVNODE from the file server.

Change-Id: Ib74300568ac083e39506b0d106a5984e8fe5e464
Reviewed-on: http://gerrit.openafs.org/5120
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>