Issue #2678822 by DamienMcKenna, David_Rothstein, stefan.r, Berdir: Drupal...

Issue #2678822 by DamienMcKenna, David_Rothstein, stefan.r, Berdir: Drupal 7.43 / 8.0.4 regression: When an anonymous user submits a form with an un-uploaded file that leads to a validation error, the file is lost on the next correct submission

(cherry picked from commit c74f0424)