Double Zero; I feel quite sure the pilot of the Skyraider would know the effect of an asymmetric flap.
He would be able see that the upper surface of the flap was undamaged and some way away from the missing wingtip.
If the aircraft had started rolling as the flaps were lowering and he was unable check the roll, he would have undoubtably very quickly. moved the flap lever back to the UP position.