NotEmptyValidator not working for radios and file inputs

[rkrahnen]

The commit from #155 has the consequence that at least for radio buttons and file uploads the marking as mandatory field does not work anymore. Both elements have no request arguments if nothing was selected or uploaded, so the condition applies to these elements. As a result, the elements are not validated afterwards.

If you remove the condition, the validation works again. But this is surely not desired, so I looked a little further and if you move the line $registerPropertyPaths($element->getIdentifier()); to the beginning of the loop, the validation works as well. If I'm looking at this correctly after the short time, that should both solve the problem without breaking the change from #155.