Windows: Fake scache not completely initialized

Windows: Fake scache not completely initialized

The fake scache object used for pioctl operations was not
fully initialized.  The magic value, data version, and
several locks were not initialized.  Do so.

Since the fid of the fake scache object is 0.0.0.0
remove the assert in cm_GetSCache for cell != 0.
Instead simply return CM_ERROR_INVAL.

LICENSE MIT

Reviewed-on: http://gerrit.openafs.org/406
Reviewed-by: Asanka Herath <asanka@secure-endpoints.com>
Tested-by: Asanka Herath <asanka@secure-endpoints.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>