Fix WorkerACLMixin get_max_level when the worker does not have a repository

arkindex/project/mixins.py

@@ -99,6 +99,8 @@ class WorkerACLMixin(ACLMixin):
     def get_max_level(self, worker):
         # Access right on a worker can be defined by a right on its repository
         worker_level = get_max_level(self.user, worker)
+        if not worker.repository:
+            return worker_level
         repo_level = get_max_level(self.user, worker.repository)
         return max(
             filter(None, (worker_level, repo_level)),