v2.0.11: Avoids validation issues during AJAX select processing

Adds a check to prevent validation errors when processing AJAX select inputs,
specifically addressing an issue where only partially rendered form values
were available during validation.

This resolves a problem encountered with Sobit pokladna, where
`$form->getUntrustedValues()` returned values only from already rendered
inputs, leading to incomplete data during validation when AJAX selects
were involved.