Fix - Validation for mandatory multiple dropdown

[RomainLvr]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes !37010
• Here is a brief description of what this PR does

If a required multiple dropdown field is present in our ticket form, it is currently possible to create a ticket without selecting any values.

The issue comes from the validation function, which only checks if a required field is empty but does not properly handle multiple-selection fields. For a standard dropdown, the function considers a value of 0 as empty. However, for a multiple dropdown, an unselected field results in an empty array, which is not detected as invalid.

A specific condition must be added to check if a required multiple-selection field is empty by detecting empty arrays during validation.

Screenshots (if appropriate):