Windows: AFSRDFSProvider NPOpenEnum vs no redirector

If there is no redirector device present, return WN_NO_NETWORK
to indicate that this network provider is not ready for browsing.

Reviewed-on: http://gerrit.openafs.org/10523
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 1e24762a2cf6590798aa9ce483a1374466c7847b)

Change-Id: Ic46a279f7ac836a83e024f0b842039249bdeaeaa
Reviewed-on: http://gerrit.openafs.org/10535
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>