By Michel Rose PARIS (Reuters) – French President Emmanuel Macron warned of the risk of a Brexit-style election upset in his only campaign rally before the first round of the presidential election, in a bid to convince dispirited voters and re-energise a lacklustre campaign. A week or so before the April 10 vote, Macron finds himself on the defensive, with far-right leader Marine Le Pen staging a comeback in the polls and the race tightening between the two frontrunners for the crucial April 24 runoff. “Look at what happened with Brexit, and so many other elections: what looked improbable actu…