THE painting promptly reminded one of the pictures formerly being peddled on sidewalks, in subject matter as well as quality. It portrayed a ramshackle cart with two oxen on both sides and a man wearing a sunhat near it. It’s in the painting style of mooi indie (fine Indies) adopted by self-taught artists like Santoso, the painter, in 1965. What’s surprising was not the painter, but rather its owner, Oei Hong Djien, 70, a painting collector w