Purpose
=======
Fix the traceback which was appearing when toggling
as done the content in the course template.
Specification
=============
The traceback happened because when all the content in the
section has been completed, we want to collapse the next section
automatically. However in this view the sections aren't
collapsable which resulted in calling methods on null HTML elements.
Fixing this by checking if HTML elements exists before trying to
collapse the next section.
Task-3449558
closesodoo/odoo#130633
X-original-commit: 51f82b306ed12dc2c8e32d2a0bd3052f8eed5d2a
Signed-off-by: Stéphane Debauche (std) <std@odoo.com>