If the right click happens on an item that is already selected,
don't pass on the signal so the selection which may span across
multiple files is kept.
Otherwise, pass on the signal which means the item under the cursor
will be selected.
This currently misbehaves (as in: doesn't work) with IconView
properly.
This could theoretically lead to infinite recursion, but only
in case "/" is inaccessible or something. In which case the user
has really bigger problems.
