By Philip Blenkinsop BRUSSELS (Reuters) – The European Commission is willing to negotiate trading arrangements for Northern Ireland with Britain, but only if talks are constructive and do not resume with an outcome already set by London, a top EU official said on Wednesday. “Our doors are open for negotiations but it has to be constructive negotiations and it cannot be done in a way that we negotiate but the result is given in advance,” Commission Vice President Maros Sefcovic told a news conference in Brussels. Sefcovic delivered a speech in London later on Wednesday, two days after legislati…