MADRID, May 23 — Spanish Prime Minister Pedro Sanchez defended his wife against graft allegations yesterday, just days after Argentina’s president sparked a diplomatic row by calling her “corrupt” at a conference of far-right leaders in Madrid. Last month a judge opened a preliminary criminal inquiry into suspicions that Begona Gomez had used her position to peddle influence, based on a complaint by an anti-graft pressure group, Manos Limpias (C…