[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.

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)
embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js