File two flats (in the plane of the screw slot) across the protruding end and grip with a pair of pliers - if this fails; which it might because you don't have much to play with, then gently dig the screw out and fill the hole with wood scraps when you come to attach the door.
Failing that just ignore the broken screw - the door will very probably be fine with just one screw missing.
Good luck
Peccavi
September 2009