Fixed serious bug killing at least short-text questions in inclass exam
The bug was introduced in [1], by testing for the existence of the disabled attribute, and when it exists, it was omitting values reading. The problem is that when form-fields are reset, the "disabled" attribute is set to 0, leading the exists check to succeed. In essence, This change sets now the default value of the form-field to "0", such that it is safe to test it everywhere. Originally, it was not set by default to save resources (memory and processing power), but this requires a more careful analysis when changes happen.