Inline validation JavaScript for z3c.form only sends request when field ...

...name can be obtained from DOM for a widget (#13741).

Note: I propose this get merged first to 4.3.x branch, then merged appropriately to master.  

Related:
https://dev.plone.org/ticket/13741
https://github.com/plone/plone.app.z3cform/pull/11

Between this pull request and the one on plone.app.z3cform, there should be increased robustness in validation on the view and better behavior on the JavaScript client-side.