Fix event handling for subelements (e.g. checkboxes for boolean fields)

The patch from #2 did work for boolean fields, but broke other field types. This patch works with both.

Thanks @sander-wemagine!
I can confirm that this updated patch works.

Hi, please create a fork and prepare a merge request, so I can review and merge it
thanks!

Here are instructions:
https://www.drupal.org/docs/develop/git/using-gitlab-to-contribute-to-dr... →

I'm sorry, I currently don't have time to do that. Anyone else wants to do that?