block the "Ask a question" button if the "subject" field of the form is not filled

please block the "Ask a question" button if the "subject" field of the form is not filled http://prntscr.com/up30c5, otherwise you write-write a question, leave the field with the topic for later, check the box, the "ask a question" button is activated, you think that everything is ok, you poke it and .... oh Gods .... everything is gone! the request is allegedly being created, but it is impossible to find it anywhere to correct it. I ask you to correct the ban / notification on the creation of a request if the topic is not filled