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.

Change-Id: I3e33769bb2d52a59b0ff993aa07e89d959d60800
Reviewed-on: http://gerrit.openafs.org/10523
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: RDR capture Cc/Mm exceptions do not break

All of the Cc and Mm functions are wrapped in try/except blocks.
The purpose is to ensure that Cc and Mm do not return an error as
an exception which could result in the afs redirector failing to
release a resource.   Instead of calling the AFS exception handler
just handle the exception with EXCEPTION_EXECUTE_HANDLER.  This permits
the __except block to capture the exception code.

The AFS exception handler will throw its own exception if the
AFSDebugFlags AFS_DBG_BUGCHECK_EXCEPTION bit is set.  This is helpful when
debugging exceptions thrown by errors in the afs redirector code.  It is
not helpful when a Cc function throws an exception.  For example,
CcReadCopy() will throw STATUS_DELETE_FILE as an exception if an attempt
to read from a deleted file is initiated.   This should simply fail the
read operation not BSOD the system.

Change-Id: I2fd1d4db530600441272e59353fbf28b831e2691
Reviewed-on: http://gerrit.openafs.org/10524
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>