Load a job record that holds unknown fields

A downgrade of Bindery no longer stops at the start.

tests/test_jobs.py

@@ -1,5 +1,6 @@
 """The job queue: shared jobs, order, cancelling and the job history."""
 
+import json
 from datetime import datetime, timedelta
 
 from bindery import config
@@ -167,3 +168,10 @@ def test_the_api_form_of_a_job_hides_the_path_of_an_upload():
     job = Job(mode=DownloadMode.IMPORT_FILE, options={"path": "/config/uploads/x.epub", "name": "x.epub"})
     assert job.to_dict()["options"] == {"name": "x.epub"}
     assert Job.from_record(job.to_record()).options == job.options
+
+
+def test_a_record_of_a_newer_bindery_loads_without_its_unknown_fields():
+    job = Job(mode=DownloadMode.NEW, story_id=3)
+    record = json.dumps({**json.loads(job.to_record()), "priority": 5})
+    loaded = Job.from_record(record)
+    assert (loaded.id, loaded.story_id, loaded.mode) == (job.id, 3, DownloadMode.NEW)