3487412: Fix WSOD when EventInstance has invalid translation.
I have a site, where an eventinstance somehow ended up in a wrong translation state. That means that now, I'm stuck - unable to edit, delete nor view the eventseries.
I cant even use "drush entity:delete" as it fails:
InvalidArgumentException: Invalid translation language (da) specified. in Drupal\Core\Entity\ContentEntityBase->getTranslation() (line 903 of core/lib/Drupal/Core/Entity/ContentEntityBase.php).
I've debugged my way to /src/Plugin/ComputedField/EventInstances.php where I can see that we use ->getTranslation without checking if it exists.
Closes #3487412