EntityTranslationController::entityFormAlter will produce following warning when translations was enabled after entity creation:
Warning: Invalid argument supplied for foreach() in Drupal\translation_entity\EntityTranslationController->entityFormAlter() (line 244 of /var/www/drupal8/core/modules/translation_entity/lib/Drupal/translation_entity/EntityTranslationController.php).
Attached patch adds extra check for the $entity->translation array.
