Open this photo in gallery: This 2019 file photo shows Canadian Robert Lloyd Schellenberg during his retrial on drug trafficking charges in the court in Dalian in China's northeast Liaoning province.Supplied/AFP/Getty Images Robert Schellenberg, a Canadian convicted on drug offences in China whose sentence was controversially upgraded to a death penalty amid a diplomatic spat with Ottawa, is at risk of being executed, advocates fear, after The Globe and Mail revealed China put to death four other Canadians earlier this year. Mr. Schellenberg was first arrested in 2014 and accused of being involved in a scheme to export 222 kilograms…