mod_assign_get_submissions and mod_assign_get_grades incorrectly check permissions

Note To be tested only in 36_STABLE and master. For 35_STABLE it's enough if automated tests are passing, so no action needed there. Prerequisite Moodle mobile app. Your Moodle mobile app should be able to connect to your Moodle website. You can either do the following: Ensure that the phone with the mobile app and the web server are on the same network. Or Expose the web server over the internet via ngrok. Test As admin, enable "Mobile services": Site administration ► Mobile app ► Mobile settings Enable "Context freezing": Administration >Development > Experimental >Experimental settings Create a new course Enrol one user as student in the course and another one as teacher Create a new assignment activity, configured to allow only "Online text" submissions As the student user, log in into the Moodle site, go to the assignment activity, and do a submission As the teacher user, log i into the Moodle site, go to the assignment activity and grade the submission the student did Now, in the assignment main page, go to settings (via the cog) and click on "Freeze this context" As teacher, log in to the site via the Moodle Mobile app, open the assignment activity, and check that you can see the submission the student did and the grade the teacher gave.