LONDON, Sept 13 (Reuters) - Whether China has become "uninvestable" or not, avoidance of the world's second-largest economy suggests the economic and political risks there have simply become too hard to assess.U.S. Commerce Secretary Gina Raimondo's trip to China last month had promised some economic and trade detente between the two superpowers now at loggerheads. But it was quickly defined by her comment that more and more U.S. firms see China as "uninvestable" amid spying, fines, raids and other risks.While bricks-and-mortar investment, supply-chain exposure and stock listings have been under...