If there are no folders present, show only the "Add Folder" button, and
hide the "Rescan All" button. Only show the latter when at least one
folder exists.
Signed-off-by: Tomasz Wilczyński <twilczynski@naver.com>
The button does nothing when the External Versioning is being used, so
it should not be displayed at all to avoid confusing the users.
Signed-off-by: Tomasz Wilczyński <twilczynski@naver.com>
