Hong Kong International Airport, buffeted by months of civil unrest in the city, has no plans to cut back on long-term investment despite air traffic slumping at one of Asia’s busiest gateways.Although HKIA has made huge investments, notably on a HK$144 billion (US$18.46 billion) third runway, the Hong Kong Airport Authority’s executive director for engineering and technology Ricky Leung Wing-kee on Thursday shrugged off the downturn in passenger traffic.Leung, in his first day on the job, was…