Route Entity data producer with non-existing translation

[artemvd]

This plugin tries to load entity translation based on the language argument. But in case that translation doesn't exist Drupal's ContentEntityBase class throws exception Invalid translation language ($langcode) specified. .

I suggest to add check if translation exists before trying to get it.

[artemvd]

PR: #1323

[hchonov]

If the entity has been requested in a specific translation, that the entity does not have then I agree that the return value should be NULL since we cannot actually resolve the requested set of parameters.

[jacintocapote]

This looks like a perfect approach and is working perfect.

[vermario]

hi! I think this is a great fix, the same code exists though also in the EntityLoad and EntityLoadByUuid plugins, so I made a new PR: #1388 .