Size does matter! The 400-pound Queens pedestrian who crashed through an Upper East Side sidewalk said yesterday that a thinner woman might have died from that fall. “Thank God, they said that my size was the only thing that saved me,” Ulanda Williams, 32, told The Post as she was discharged from NewYork-Presbyterian Hospital. Williams, of Springfield Gardens, was waiting for a bus at about 9:10 p.m. Friday when she tried to hide from the rain under an awning. The ground suddenly disappeared beneath her — and she was swallowed whole by the cavernous space adjacent to the cellar of...