[Form] fixes empty file-inputs get treated as extra field
[template] fixed test failure introduted from #8585
Merge branch '2.3'

* 2.3:
  [Form] fixes empty file-inputs get treated as extra field
  return 0 if there is no valid data
  [DependencyInjection] fixed regression where setting a service to null did not trigger a re-creation of the service when getting it
  [DependencyInjection] fixed #8570
  fixed file permission
  The ignoreAttributes itself should be ignored, too.
  [Tests] Tests on php 5.5 should pass
  [Twig] fixed TwigEngine::exists() method when a template contains a syntax error (closes #88546)