Can't submit portfolio via LTI 1.1

[Kristina Hoeppner]

I ran into this problem on Mahara 22.04 and main, which I tested on two sites:

When assignment submission via LTI 1.1 is set up in Moodle 4.0 (via the 'External tool' option), I can't submit a portfolio because I get the following error message:

[WAR] 64 (lib/errors.php:530) [Error]: Cannot access protected property ModuleLtiSubmission::$timegraded at /var/www/master-dev-prod-mahara/releases/20220503181248/module/lti/submission.php:73
Call stack (most recent first):

    exception(object(Error)) at Unknown:0

To replicate:

1. Set up LTI 1.1 on Moodle with the connection to Mahara.
2. Create an 'External tool' activity in a Moodle course using that connection.
3. As teacher, click the activity link and set the activity conditions in Mahara.
4. As student, click the link to the activity. If you already have an account and a portfolio, you can select it.

Results:
- Expected: Your portfolio is submitted.
- Actual: The above error message occurs.

[Mahara Bot (dev-mahara)]

Patch for "main" branch: https://reviews.mahara.org/c/mahara/+/12703