handle sites for which maint status does not exist

Author: kthare10

fabric_cf/actor/core/container/maintenance.py

@@ -177,6 +177,9 @@ def is_sliver_provisioning_allowed(*, database: ABCDatabase, project: str, email
         """
         status, site = Maintenance.is_site_in_maintenance(database=database, site_name=site)
 
+        if not status and site is None:
+            return True, None
+
         projects = site.get_properties().get(Constants.PROJECT_ID)
         users = site.get_properties().get(Constants.USERS)