Alibaba stock is down 26% this year. Greg Baker/AFP via Getty Images Alibaba , NIO , and a handful of other U.S.-listed Chinese stocks got off to a rocky start Tuesday, dragged down by worries about new Covid-19 lockdowns in China—and what that might do to the world’s second-largest economy. The stocks had a rough time on Monday, too —on Hong Kong’s Hang Seng Index. U.S. markets were closed Monday for Labor Day. By midday, shares in e-commerce giants Alibaba (ticker: BABA) and JD.com (JD) were off 3% and 2.5%, respectively. NIO ( NIO ), the electric-vehicle maker, was down…