If you have a toddler who loves to open the shower door on you, then print a lock for the door! The odds of this fitting your exact handle are slim, but hopefully it'll get you started on designing your own.

Print the shower-door-insert-flipped.stl first. Then insert it into shower-door.stl (circular tabs down into the corresponding recesses) a few layers after if finishes printing the groove that the shower door handle slides into. The next layers will lock the insert into place and you won't have to worry about any tricky bridging.