Tokyo stocks were flat Tuesday morning, as buying on dips amid continued optimism about Japanese equities offset moves to lock in gains after a recent rally. The 225-issue Nikkei Stock Average fell 49.72 points, or 0.12 percent, from Monday to 40,364.40. The broader Topix index was up 3.58 points, or 0.13 percent, at 2,781.22. The U.S. dollar moved narrowly in the lower 151 yen range in Tokyo amid wariness over a possible yen-buying intervention by Japanese authorities, dealers said. At noon, the U.S. dollar fetched 151.33-34 yen compared with 151.37-47 yen in New York and 151.32-33 yen in Tok…