fix: avoid resetting a learner schedule to before a course starts

If a learner changes modes (like upgrades to a verified learner),
we will reset their schedule for them. But if they did this before
the course started, we would accidentally set their schedule to
the current time. So when the course did start, they would already
appear to be behind schedule.

That's silly. So now we always look at course start time when
resetting the learner's schedule.

AA-426

openedx/core/djangoapps/schedules/utils.py

@@ -34,7 +34,7 @@ class PrefixedDebugLoggerMixin:  # lint-amnesty, pylint: disable=missing-class-d
         LOG.info(self.log_prefix + ': ' + message, *args, **kwargs)
 
 
-def reset_self_paced_schedule(user, course_key, use_availability_date=False):
+def reset_self_paced_schedule(user, course_key, use_enrollment_date=False):
     """
     Reset the user's schedule if self-paced.
 
@@ -44,7 +44,7 @@ def reset_self_paced_schedule(user, course_key, use_availability_date=False):
     Arguments:
         user (User)
         course_key (CourseKey or str)
-        use_availability_date (bool): if False, reset to now, else reset to when user got access to course material
+        use_enrollment_date (bool): if False, reset to now, else reset to original enrollment creation date
     """
     with transaction.atomic(savepoint=False):
         try:
@@ -56,10 +56,13 @@ def reset_self_paced_schedule(user, course_key, use_availability_date=False):
         except Schedule.DoesNotExist:
             return
 
-        if use_availability_date:
-            enrollment = schedule.enrollment
-            schedule.start_date = max(enrollment.created, enrollment.course.start)
-            schedule.save()
+        if use_enrollment_date:
+            new_start_date = schedule.enrollment.created
         else:
-            schedule.start_date = datetime.datetime.now(pytz.utc)
-            schedule.save()
+            new_start_date = datetime.datetime.now(pytz.utc)
+
+        # Make sure we don't start the clock on the learner's schedule before the course even starts
+        new_start_date = max(new_start_date, schedule.enrollment.course.start)
+
+        schedule.start_date = new_start_date
+        schedule.save()