The XDG Documents Portal's FileTransfer does not appear to support directories,
instead it silently drops them. In case the MIME data has mixed files and
directories, this results in the directories being silently dropped from the
result.

This can be seen in Dolphin: try copying a file and a directory. Pasting will 
only paste one item.

With this change, we don't portalize the URLs if they have any directories in them.