Steps to reproduce:

1. Install https://moodle.org/plugins/quizaccess_honestycheck (standard quiz Password access restriction may also work)
2. Create a quiz using that access restriction
3. Click "Start attempt"
4. Complete the form that pops up.
5. Answer one question (not essential).
6. Click "Start another preview"
7. Now, on the start attempt form, click cancel.

Actual result: You are on the quiz view.php page. In the table that lists your attempts, you can see your old preview, with a sumbitted date of 1st Jan 1970 (unix date 0).

Expected result: Something else. Either the preview should already be deleted, or perhaps we should use Abandoned state, rather than Finished.