Windows: only flush buffers on shutdown if running

Windows: only flush buffers on shutdown if running

If a service shutdown message is received prior to the
service entering the running state, do not attempt to
buf_CleanAndReset() because the required data structures
and locks are not initialized.

Change-Id: I29f20dbe91230f078334ca58e8791d2422cdecfd
Reviewed-on: http://gerrit.openafs.org/5733
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>