Display error message when try to skip steps with unfilled required fields

As in README:

You may directly access a step by adding ?step={step_name} to the current url. E.g.: node/1/edit?step=step_article_additional will jump to the step named
"step_article_additional".
If there are steps with unfilled required fields (step is "not skippable") the first non-skippable step will be displayed instead of the one requested by url.

This is a great feature, but it would be even better if an error message was displayed to the user.