EZP-23643: Search without permissions throws UnauthorizedException

https://jira.ez.no/browse/EZP-23643

After refactoring of SearchService for performance in 5.3.3, turning on permission filtering via $filterOnUserPermissions now throws UnauthorizedException because of $contentService->loadContent() use.

The reason this was not caught was because the integration tests testing this has been disabled for a long time (since search was moved from Content Service, so pre 5.0). Found when fixing skipped tests in first commit here.
The comment is incorrect, Content 12 is actually "Administrator users" user group.