fix debug notice when creating a post

[t-schroeder]

Got this debug notice when creating a discussion:

Fields list in snapshot record does not match fields list in 'hsuforum_discussions'. Record is missing fields: timelocked
line 863 of /lib/classes/event/base.php: call to debugging()
line 248 of /mod/hsuforum/classes/service/discussion_service.php: call to core\event\base->add_record_snapshot()
line 104 of /mod/hsuforum/classes/service/discussion_service.php: call to mod_hsuforum\service\discussion_service->trigger_discussion_created()
line 180 of /mod/hsuforum/classes/controller/edit_controller.php: call to mod_hsuforum\service\discussion_service->handle_add_discussion()
line ? of unknownfile: call to mod_hsuforum\controller\edit_controller->add_discussion_action()
line 124 of /mod/hsuforum/classes/controller/kernel.php: call to call_user_func()
line 89 of /mod/hsuforum/classes/controller/kernel.php: call to mod_hsuforum\controller\kernel->generate_response()
line 83 of /mod/hsuforum/route.php: call to mod_hsuforum\controller\kernel->handle()