Fix nxu:inputFile postback when placed after an immediate field with a validation error

Steps to reproduce:

• on a File-like document, add a required select2 (like the "nature" widget) before the field upload
• create a document, do not fill the required select2, and chose a file
• submit
  => the upload radio button is still checked but uploaded file is lost.

Instead, the "keep" button should be checked and uploaded file shown.

Note pb does not appear when producing a validation error on the "title" field.