By Joseph Ax (Reuters) – Early voting began in Ohio on Tuesday for the May 3 primary elections, all but ensuring that voters will pick their candidates for the U.S. Congress using a Republican-backed congressional map despite ongoing litigation over its legality. The state Supreme Court in January threw out a previous iteration of the map, ruling that it violated a state constitutional provision barring congressional districts drawn to benefit one party over another, a practice known as gerrymandering. In response, the Republican-controlled state redistricting commission, including Republican …