By Yimou Lee and Martin Quin Pollard TAIPEI/BEIJING (Reuters) -U.S. House of Representatives Speaker Nancy Pelosi was set to visit Taiwan on Tuesday, three people briefed on the matter said, as China warned that its military would never “sit idly by” if she visited the self-ruled island claimed by Beijing. Pelosi, who began an Asia trip earlier on Monday in Singapore, was due to spend Tuesday night in Taiwan, the people said. Taiwan’s foreign ministry said it had no comment on reports of Pelosi’s travel plans. Amid widespread speculation over whether she would make a stop in Taiwan, Pelosi’s o…