Fix EZP-22228: NotFoundException thrown when not all requested languages are present

https://jira.ez.no/browse/EZP-22228

When passing a language filter to `ContentService::loadContent()`, and requested content isn't translated in one of the passed languages, `ContentService` will throw a `NotFoundException`, even if the content exists in at least one of the passed language.
This is a blocker when using prioritized languages. It should not throw an exception for this since the `ContentHandler` (SPI) is already reponsible of throwing a `NotFoundException` if there is no result.

This issue appeared after merging #686