Fix: pass when no CF value is selectable for a CF depending on another CF's value

[brunetton]

Hi

This PR fixes a case we had to handle in one of our client's RT instance.
First of all, I'm sorry not to have written tests for this particular case; I'm don't feel yet comfortable enough to write tests for RT.

The problem fixed here appears when a CF that values depends on another CF's values have no selectable value.
The plugin block from validating transition, requireing a value for the CF that do not exists.

Steps to reproduce problem

• define a CF named cf1 with values:

  • value 1
  • value 2

• define another CF named cf2 with only one value, based on cf1 value:

  • cf1 -> value 1 => cf2 -> value 1

• define rules for MandatoryOnTransition plugin that implies both cf1 and cf2:

  Plugin('RT::Extension::MandatoryOnTransition');
  Set(%MandatoryOnTransition,
     'MandatoryOnTransitionTest' => {
         '* -> resolved' => ['CF.cf1', 'CF.cf2'],
         '* -> open' => ['CF.cf1', 'CF.cf2'],
     }
  );
  

• change status of a test ticket, selecting value 2 for cf1

  • => no values are presented for cf2, as there is no possible values for this CF in that case

• try to validate page => MandatoryOnTransition blocks from validating, saying that a value must be selected for cf2