By MAE ANDERSON Cost cuts helped Staples Inc.' second-quarter net income rise 40 percent as revenue remained flat as Americans and small businesses spent cautiously on office supplies.The nation's biggest office supply chain said Tuesday that net income for the three months ended July 31 rose to $129.8 million, or 18 cents per share, from $92.4 million, or 13 cents per share, last year.Net income was 20 cents per share excluding a restructuring charge.