Windows: Fix usage of cm_FreeServerList

Windows: Fix usage of cm_FreeServerList

cm_FreeServerList will set the input variable to NULL if the
contents of the list could in fact be freed.  If they could not
be freed, the individual entries are marked for deletion and will
not be subsequently used.  Do not set the list variable to NULL
after calling cm_FreeServerList otherwise memory can be leaked.

LICENSE MIT

Change-Id: Ia3cacd760d7395a2dd6b063643a8aa86f9e468b9
Reviewed-on: http://gerrit.openafs.org/2078
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>