Windows: Fix cm_AppendServerList

Should use || and not | as the operator when testing for
NULL pointers.

Change-Id: I00afe64aec4f965d6a831028b546ed01d8e9672a
Reviewed-on: http://gerrit.openafs.org/11523
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>