Windows: KFW_AFS_get_cred fail on error

If KFW_AFS_klog() fails and there is no password set, then goto
cleanup.

Change-Id: Iba3980c699b9a9b3de078d9187de40114bc33daf
Reviewed-on: http://gerrit.openafs.org/10224
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>