EZP-21976 Fix empty binary file field returning "()"

link: https://jira.ez.no/browse/EZP-21976

Fixed "()" when we call ez_render_field() on a empty binary file.

Notice that I couldn't use ez_is_field_empty() which use for parameters a 'content' and a 'field' in 
/ezpublish-kernel/eZ/Bundle/EzPublishCoreBundle/Resources/views/content_fields.html.twig, 
because the template doesn't have 'content' but only 'contentInfo' .