No validation error is shown when not entering other researchers

[tijmenbaarda]

Path: /proposals/other_researchers/
Occurred during practice application.

When selecting "yes" but not entering other researchers, no validation error is shown but the user cannot continue.

The same happens when I do add another researcher, but when I also remove myself.

[tijmenbaarda]

Probably related to this, when first selecting "yes" and then "no" to the first question, it seems that the (now invisible) researcher list is still evaluated, so the same problem as above occurs.

[miggol]

Can be grouped together with #728

[EdoStorm96]

It seems that the widget we are using for this (SearchableSelectWidget), does not display errors ... This also happens with the supervisor field. I've made an issue in the DSC for this.

For now, the fix is, I would say, to display these error on another field.