Form validation can be skipped

neos/forms is an open source framework to build web forms. By crafting a special `GET` request containing a valid form state, a form can be submitted without invoking any validators. Form state is secured with an HMAC that is still verified. That means that this issue can only be exploited if Form Finishers cause side effects even if no form values have been sent. Form Finishers can be adjusted in a way that they only execute an action if the submitted form contains some expected data. Alternatively a custom Finisher can be added as first finisher. This regression was introduced with https://github.com/neos/form/commit/049d415295be8d4a0478ccba97dba1bb81649567