weather: Handle missing permission store

weather: Handle missing permission store

Our weather integration is supposed to follow GNOME Weather's settings,
including its permission to use location services. However there's a
discrepancy in case xdg-desktop-portal is unavailable:

While our geoclue agent grants all applications access to location
services in that case, the weather integration treats it as if
access was denied.

Fix this by handling this case explicitly.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/1130