The Everest climbers who disappeared on a mission 100 years ago had problems with their oxygen tanks, a new book has claimed. George Mallory, 37, and Andrew 'Sandy' Irvine, 22, went missing during their 1924 expedition to climb the world's tallest mountain. Mick Conefrey, in his upcoming book Fallen, George Mallory: the Man, the Myth and the 1924 Everest Tragedy, …