Windows: Protect against cm_GetVolServerList failures

In cm_Analyze, if cm_GetVolServerList() fails volServerpp will be
NULL which will trigger an exception if passed to either
cm_SetServerBusyStatus or cm_ResetServerBusyStatus.

Reviewed-on: http://gerrit.openafs.org/9960
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit dfd74696844df7ffacc5c2db01393bad3fce9dcc)

Change-Id: I4224cc0b82ba91e347f20be7442584e19014f364
Reviewed-on: http://gerrit.openafs.org/9961
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>