Coding error detected, it must be fixed by a programmer: start_progress() max value cannot be zero or negative

More information about this error
Debug info:
Error code: codingerror
Stack trace:

line 91 of /backup/util/progress/core_backup_progress.class.php: coding_exception thrown
line 176 of /backup/util/plan/base_task.class.php: call to core_backup_progress->start_progress()
line 173 of /backup/util/plan/base_plan.class.php: call to base_task->execute()
line 167 of /backup/util/plan/restore_plan.class.php: call to base_plan->execute()
line 343 of /backup/controller/restore_controller.class.php: call to restore_plan->execute()
line 184 of /backup/util/ui/restore_ui.class.php: call to restore_controller->execute_plan()
line 74 of /backup/restore.php: call to restore_ui->execute()

The same error can be encountered both when backing up a course and restoring a course.

To reproduce on backup:

1. Log in as an admin.
2. Browse to a course with several sections and activities in each.
3. Start to produce a back, when you get to the step where you can select what sections/activities to include unselect all but one section and its activities.
4. Attempt to complete the backup.

To reproduce on restore:

1. Backup the course above with all default (will complete fine)
2. Start to restore merging into an existing course.
3. On the screen where you can select what sections/activities to restore unselect all but one section and its activities.
4. Click continue. Boom!