Added an additional check so back has to be pressed twice on the root
folder to actually leave the application. It's a check seen in many
other apps.

Change-Id: I26827113a41070aa8188fa616ba8fe53742329b3
Reviewed-on: https://gerrit.libreoffice.org/16245Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Jacobo Aragunde Pérez <jaragunde@igalia.com>