If the folder is unversioned, Subversive tries to load it more than once (bug 471205)

https://bugs.eclipse.org/bugs/show_bug.cgi?id=471205

git-svn-id: https://dev.eclipse.org/svnroot/technology/org.eclipse.subversive/trunk@21488 ee007c2a-0a25-0410-9ab9-bf268980928c