Windows: _._AFS_IOCTL_._ size is zero

Windows: _._AFS_IOCTL_._ size is zero

When replying to a FileStandardInformation query on the pioctl
special file, the size of the file is 0.  Failure to return 0
can result in an anti-virus program attempting to read the file
via a paging request which will fail.

Change-Id: I83f2f40cca99c04a5fe06546f19bdf96dfbb4951
Reviewed-on: http://gerrit.openafs.org/6109
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>