For that corner, or any corner where its not quite a large enough bit of damage to warrant just cutting out the corner and adding in a new piece of wood.. I've had good results adding in either a bit of wooden doweling rods, or some screws to act as a sort of as rebar for when i formed bondo around it, just to give it a little bit of strength/durability. If you try to rebuild the corner from just bondo alone , at some point in the future if it happens to gets a bit of force on that corner (getting kicked or banged around), it might just snap out the chunk of bondo. I used screws on my Joust corner touchup a few years back, wish I took pictures of it, but its held up great, and you'd never know it was repaired that way.