Force query to list before passing as argument

An unevaluated query ends up being used as an argument of intended list
type to another query, which fails in the case of an EmptyQuerySet, which
is not iterable.

snf-astakos-app/astakos/im/functions.py

@@ -920,5 +920,5 @@ def qh_sync_projects(projects):
 
 def qh_sync(user_ids):
     users = AstakosUser.forupdate.filter(id__in=user_ids).select_for_update()
-    astakos_quotas = users_quotas(users)
+    astakos_quotas = users_quotas(list(users))
     set_user_quota(astakos_quotas)