If no rules file is given, simply re-use the previous one. If no RF is given
the first time this function is called, use the built-in default.
This includes fixing the built-in default to something that actually exists.
Signed-off-by: Peter Hutterer <peter.hutterer@redhat.com>
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>

Fixes ArcticaProject/nx-libs#371