Depends on a number of things, including if the block walls are concrete-filled, properly doweled into the slab/footings, and even estimated high wind loads in your area (for anticipated shear forces on the corner). You should try to determine if the first two points are valid before proceeding, otherwise you could face future problems from the forces a slamming door places on an improperly-constructed block wall. If you choose not to do any exploratory investigation, you can always gamble by installing the door anyway, but I'd suggest locating it as far away as possible from the corner. Either that, or build a few reinforced concrete exterior balusters if you choose to crowd the corner. Could even get fancy and build a covered archway entry there.