Usually the service’s organisation and the user’s current organisation
will be the same. But this won’t be the case when:
- someone with a non-government email address is looking at the page
- someone from our team, as a platform admin user, is looking at the
page (it will show Cabinet Office instead)
This commit fixes these problems by explicitly looking at the service’s
organisation. We couldn’t do this previously because when this page
wasn’t service-specific `current_service` was not guaranteed to be set.