MUNICH — Former Ukrainian President Petro Poroshenko has two key pieces of advice for anyone negotiating with Vladimir Putin. First and most importantly, never trust him; and second, only start talking to the Russian leader when you’re arguing from a position of strength. Poroshenko fears those maxims are being ignored in the current U.S.-brokered peace talks on Russia’s war, he told POLITICO in an interview in Munich. Poroshenko, Ukraine’s so-called Chocolate King, is guided by his experience