Fix JENKINS-22199

Issue is that the logentry path is not a child of the folder which is referenced as external folder.
So the change is unrelated and should remain untouched (or left out).

I updated the testcase to include the failing situation, after that I fixed the issue in DirAwareSVNXMLLogHandler

(unfortunately I used the wrong Jenkins ticket number in the Git commit, title of the pull request is right.)