Two months after losing an appeal against his conviction and sentence for sexually assaulting his son’s nine-year-old friend during a Halloween sleepover in 2015, a former chief executive of a multinational company has been certified unfit for caning in Singapore.The 49-year-old foreign national, who returned to the High Court in a wheelchair on Tuesday, was last year sentenced to 14 years’ jail and the maximum 24 strokes of the cane. He lost his appeal in August.However, prison doctors found…