The bidding for Lot 17 started at $23 million. In the packed room at Sotheby’s in Manhattan, the price quickly climbed: $32 million, $42 million, $48 million. Then a new prospective buyer, calling from China, made it a contest between just two people. On the block that evening in November 2014 were works by Impressionist painters and Modernist sculptors that would make the auction the most successful yet in the firm’s history. But one painting drew particular attention: “Still Life, Vase with Daisies and Poppies,” completed by Vincent van Gogh weeks…