Fix ghost folder when browsing WebDAV content

A ghost folder is displayed among the children of a folder when browsing with a WebDAV client :

• using Windows native tool, the ghost folder takes the place of a real folder, which prevent access to it
• using other clients like BitKinex, all the children are present, plus the ghost folder.

The problem is related to the computation of the parent URI, where the backend name is appended to the current URI, what shouldn't