Fix: MitId Children select missing a succesful check

[jekuaitk]

The MitId Children Select element ajax callback is running despite the lookup result being unsuccessful.

This results in unexpected behaviour and various errors.

[jekuaitk]

Hi @ds-bellcom

This is one of the issues we would like a review on!

[ds-bellcom]

@jekuaitk or @martinyde Review is done (2 weeks ago). Will one of you merge it and close this issue when done?

CC: @Anna-itk @ChatBotBerg