Debug time limit handling

ref-test/app/models/entry.py

@@ -86,7 +86,7 @@ class Entry(db.Model):
         self.answers = answers
         self.result = result
         write('tests.log', f'Test completed by {self.get_first_name()} {self.get_surname()}.')
-        delta = timedelta(minutes=self.test.time_limit+1)
+        delta = timedelta(minutes=int(0 if self.test.time_limit is None else self.test.time_limit)+1)
         if not self.test.time_limit or self.end_time <= self.start_time + delta:
             self.status = 'completed'
             self.valid = True