[nit] return false; when calling prevent default on event

[mrcnski]

nit I think usually you want to call prevent default on the event, but you also want to return false here. I don't know why though unfortunately, I just know onsubmit="whatever(); return false" or onsubmit="return myValidator()" is a thing. Decided to leave the comment since it might be useful to you but feel free to just resolve if we don't care.

Originally posted by @peterjan in #188 (comment)