Still high on the list of the world’s 100 best novels, Joseph Conrad’s haunting “Heart of Darkness” continues to fascinate, mystify, and attract adaptors. Although Francis Ford Coppola’s 1979 award-winning film “Apocalypse Now,” starring Marlon Brando is, arguably, the most imaginative of the lot—moving Conrad’s brooding and inscrutable Congo tale to Vietnam—the 1902 novella inspired earlier films (Boris Karloff as the charismatic Kurtz in 1958, John Malkovich in 1993). “Heart of Darkness” has