solved file_required https://github.com/globaleaks/GlobaLeaks/issues/565
changed the only error code as it creates ambiguity reading a browser debug log.
file presence checked only when submission is finalized https://github.com/globaleaks/GLBackend/pull/154
zMerge branch 'feature/file_required' of github.com:globaleaks/GLBackend into feature/file_required
Merge pull request #154 from globaleaks/feature/file_required

solved file_required https://github.com/globaleaks/GlobaLeaks/issues/565