This fix corrects problem of missing language in full.html.twig for PreviewController.

In full.html.twig is used eZ\Publish\Core\Repository\Values\Content\Content method getFieldsByLanguage without $languageCode parameter.
When we use this template in other languages than mainLanguageCode, method getFieldsByLanguage is returned empty array.

We have problem in Studio in Preview Mode ( https://jira.ez.no/browse/EZS-936 Translation problem in Studio Preview).
After clicking on Edit in one of other siteacceses than main site, we can't create proper link to edit LandingPage.
In Studio Demo, this problem is resolved in PR: https://github.com/ezsystems/EzLandingPageFieldTypeBundle/pull/145/files

In Studio (Clean) we use default Platform settings for templates. This fix solves our problem in Studio (Clean).

Steps to reproduction:

Steps to reproduction:

Requirements:
1 Install Platform clean on branch 1.4 https://github.com/ezsystems/ezplatform/tree/1.4
2 Add German ('ger-DE') language:
a) in ezplatform.yml
b) in Admin Panel / Languages / Create new Language

Steps:
1 In Admin panel go to Content / Content structure and click on Translations
2 Click on "New Translation", select "German" , check "Base ..." , select "English" and click on Publish.
3 In View tab select "German" from Language select, click on Edit and click on Preview.

Problem:
1 Preview for german version is empty (for english is OK).

Fix:
1 https://github.com/adib78/ezpublish-kernel/tree/EZP-26281-missing-language-for-preview