Windows: Only install Service NP if one exists

Windows: Only install Service NP if one exists

Do not blindly install a network provider for the service since at
least one end user organization does not install the service's network
provider.

Change-Id: I15a528ff34ffd3e060fdbd93545af3857592c835
Reviewed-on: http://gerrit.openafs.org/12051
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>