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.

#1130
Status Job ID Name Coverage
  Source Check
passed #266336
js_check

00:01:09

 
  Build
passed #266337
build

00:05:00

 
  Test
passed #266338
test

00:05:02

passed #266339
test-pot

00:05:27