samigo: Leaving null due date but setting past retract date creates erroneous submissions

SAM-2985 is a band-aid fix to prevent the following situation:
Instructor publishes assessment with a past Late submissions date and a NULL due date. Student attempts to take the test and the following occurs:

1. The student can't take the test.
2. An actual take triggers on Begin Assessment.
3. If the test is timed, this take is submitted immediately (because the assessment retract date is in the past) and the student gets an erroneous blank submission.

SAM-2985 puts in place a date check on publish such that a due date equal to or later than the late submissions date is required. However, instructors can accidentally "work around" this date check to produce erroneous student submissions. UVA has a fix to the cause of the erroneous submissions that should be contributed back.

Screencast of issue:
Authoring, producing the issue: https://www.screencast.com/t/Ldnw03R3SV
Delivery, getting 0 score submission: https://www.screencast.com/t/duuVpRvOlWJ

Steps to reproduce:

1. In a site with at least one student, create an assessment with at least one question.
2. In Settings, select the following:
   • due date = Now
   • late submissions date = Now
   • timed (and enter a time in min)
3. Click Save Settings and Publish
4. On the Publish Assessment screen do NOT publish yet. Click Edit Settings.
5. DELETE the due date.
6. At the bottom of the screen, click Save. Note: No date check ever occurs on Save because it doesn't matter what the dates are in Working Copies.
7. Samigo politely returns you to the Publish Assessment screen with the incorrect date settings saved. Click Publish.
8. Log in as a student.
9. Go to samigo and note that you can click the link to the test even though it shouldn't be available.
10. Try to access the test. Note in the begin assessment page that the late submission date is displayed.
11. Click Begin Assessment.
12. Get the "sorry it's past the late submission date" message.
13. Go back to samigo main page and find your freshly submitted, blank test. (If you didn't allow feedback in the settings, you can log in as instructor to confirm that it's 0 score also)