I worked down with Geoff Roberts for a few years and he does tons of repairs. I've seen pretty much every bodge and failure that there is, and in my opinion, it will fail. Maybe not today or tomorrow but it will go and you'll wish you hadn't bodged it.
You have a butted end on a fork steerer for a reason. You would be welding (I'm presuming TIG) on the thinnest part of the steerer and it will create a weakness.
Just my opinion but I would always replace the whole steerer.