Cathay Pacific said it expected 2020 to be a “highly challenging” year, marking little room for improvement after its business was hampered last year by several months of social unrest in Hong Kong.Unveiling its December business performance, the city’s flagship airline said its inbound traffic had fallen by almost half for the second month running.The airline group’s China business also remains significantly weak, despite this typically being one of the busiest months of the year.“We…