[web/form] Relax condition for non-translating field names
we should test true condition instead of None, so if one raise a ValidationError
using an empty string as 'no-field' marker instead of None, we don't get the PO
file header that gettext likes to return when one attempt to translate an empty
string.
Document: cubicweb-doc
Title: CubicWeb Documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/python-cubicweb-documentation/html/index.html
Files: /usr/share/doc/python-cubicweb-documentation/html/*