LocalLister: always append trailing slash if it's a folder
Summary:
We were adding the trailing slash only when recursively calling scan(),
but we need to do the same also when calling Folder::append().
Test Plan:
- filelight ~/home/foo/bar
- go up to ~/home/foo
- check whether /home/foo/bar has the trailing slash in the relevant map tooltips.
Differential Revision: https://phabricator.kde.org/D10801