Disable HTML5 validation when Save as Draft button is clicked

Having *just* committed, pushed, tagged, and cut a new release with this *apparently* oh-so-simple vanilla Javascript solution (feeling very smug, I must say), my esteemed colleague @Ambient.Impact pointed out that we can probably just use [formnovalidate](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/button#formnov...) on the button we add, and let HTML5 take care of the rest. I'm grateful and properly embarrassed that I didn't explore a pure-HTML approach further, but here we are. I'm considering reverting my earlier commit if I can prove that this approach also works :)

I've tested the formnovalidate approach and it works beautifully. I've reverted the previous commit and will add this (simpler and more universal) solution instead.

Automatically closed - issue fixed for 2 weeks with no activity.