Fix an error which caused services to be invisible to the user

feudal/backend/models/users.py

@@ -111,7 +111,8 @@ class User(AbstractUser):
             if queryset is None:
                 queryset = vo.services.all()
             else:
-                queryset.union(vo.services.all())
+                # merge querysets
+                queryset = queryset.union(vo.services.all())
 
         return queryset