Fix tree used in filter when in a user workspace

In Nuxeo Platform:

• go to a personal workspace
• click the search tab (for advanced search)
• click the location filter at the bottom

=> the filter only displays the user's personal workspace and not the root

Another way to see it:

• Do a search including a location filter
• Save the search
• Go to the home tab
• Edit your saved search

=> The location filter only points to the user's personal workspace, it should rather point to root