Submissions scores can be too quick

It's possible this score has not been logged yet, we should handle that.

TNL-6236

lms/djangoapps/grades/tasks.py

@@ -135,6 +135,9 @@ def _has_database_updated_with_new_score(
                 "item_type": "openassessment"
             }
         )
+        if api_score is None:
+            # Same case as the initial 'if' above, for submissions-specific scores
+            return score_deleted
         reported_modified_time = api_score.created_at
     else:
         reported_modified_time = score.modified