The movement of the enabling member (74) through the second arcuate path thereof is operable to allow the actuating move into the inoperative position thereof. When the enabling member (74) is in the third position thereof, it is biased to move through a third arcuate path by the release of the trigger member (42). The third arcuate path of movement of the enabling member (74) is configured to move the opposite end of the enabling member (1) into a position overlying the upper end (82) of the upper structure (84) when the upper structure (84) is disposed in the inoperative position thereof and (2) into abutting engagement with the upper structure (84) when the upper structure is in the operative position thereof.