When we changed recursive lists to use --fast-list by default this
broke listing with --drive-shared-with-me from the root.
This turned out to be an unwarranted assumption in the ListR code that
all items would have a parent folder that we had searched for - this
isn't true for shared with me items.
This was fixed when using --drive-shared-with-me to give items that
didn't have any parents a synthetic parent.
Fixes#3639