We are supposed to wait for all video + nodes processing, and return on first exception.

            futures = cf.wait(                self.videos_futures + self.nodes_futures,                return_when=cf.FIRST_EXCEPTION,            )

Log of last khan_academy_fr as reported in#100 shows that multiple nodes had to fail before the scraper stopped.

I tried to debug / fix the issue locally but it is just pure non-sense for now, there is probably a bug somewhere but I do not achieve to understand where.