Fix systemsettings randomly crashing when KCM opened
Systemsettings sometimes crashes when the KCM is opened. This had to do with passing "null" as a ref value from main.qml to the permissions page. The "null" value represents that no application is selected.
To fix this, we introduce another boolean variable, which is set to true if no application is selected and false otherwise. "ref" is no longer set to "null" in the beginning.
To test this: before pulling the changes, build it, "source prefix.sh" and then "systemsettings kcm_flatpak". Then randomly start changing KCMs. At some point (pretty early), it should crash when KCM Flatpak is opened again. Then pull the changes and do the same thing. It shouldn't crash now.