Shows episodes not existing on Trakt get marked as unwatched on every sync.

[foux]

Issue description

As we know, Trakt is now using TMDB as it's prime source, and there can of course be differences between TMDB and other sources. FOr example the series Brooklyn Nine-Nine, TMDB id 48891 and TVDB id 269586. For the last season, TMDB (and so Trakt) has 9 episodes, while TVDB has 10 (not arguing which is right and which is wrong, that's not the point, they both have valid arguments).

On my disk I've got the version with 10 episodes on season 8. And even if I locally mark the 10th as watched, it gets unwatched at every sync. The issue is off course the same each time and for other shows where the list of episodes doesn't match

Proposed fix

If an episode doesn't exist on trakt, it should be ignored by the sync, and leaved in its current watched status.

[foux]

Another example, the show I Am Groot, which is considered as a five episodes one season show on TVDB, but as five movies on Trakt. If added to a TV Shows library, gets marked as unwatched on every sync

[Shadowghost]

Most likely caused by the plugin falling back to try syncing episodes by number if no id is found or matched.
I'm curently considering removing that codepath because it's reliability has been questionable.