Patrick Frater Asia Bureau ChiefBona Film Group, one of China’s most consistently successful private sector movie studios, is in the final stages of launching an IPO on the Shenzhen stock exchange. The company was behind last year’s “The Battle of Lake Changjin,” the highest grossing film of all time in China.The IPO move represents a return to public company status for a firm that has frequently been ahead of its time.Bona was in the early wave of Chinese companies to list their share in the U.S. and achieved an IPO on the NASDAQ exchange in 2010, in the hope that U.S.