It would take someone with nerves of steel to joke about the security of Chinese smartphones in front of Xi Jinping. Step forward the South Korean president, Lee Jae Myung, who, after being given a pair of smartphones by the Chinese leader before their state banquet at the weekend, wondered out loud if the devices were secure. Xi, who is not known for public displays of humour, laughed and smiled as Lee’s quip was translated into Chinese, before displaying some sharp wit of his own. Pointing at the phones, he…