Look at service’s organisation on agreement page

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.

app/main/views/agreement.py

@@ -1,6 +1,7 @@
 from flask import abort, render_template, request, send_file, url_for
 from flask_login import current_user, login_required
 
+from app import current_service
 from app.main import main
 from app.main.views.sub_navigation_dictionaries import features_nav
 from app.s3_client.s3_mou_client import get_mou
@@ -20,8 +21,8 @@ def agreement():
 @login_required
 def service_agreement(service_id):
     return render_template(
-        'views/agreement/service-{}.html'.format(current_user.default_organisation.as_jinja_template),
-        owner=current_user.default_organisation.name,
+        'views/agreement/service-{}.html'.format(current_service.organisation.as_jinja_template),
+        owner=current_service.organisation.name,
     )