CHICAGO — Tens of thousands of visitors will pass by a 138-year-old brick church facing a parking lot for the United Center, home of this week’s Democratic National Convention. Welcoming visitors into the landmark building would be a “blessing” — and timely — given the history of Greater Union Baptist Church, which includes a visit from Black civil rights activist and suffragist, Mary Church Terrell, said Walter McCray, the Baptist church’s pastor. ALSO READ: ‘Powder keg’: Massive security presence on display in Chicago amid signs of trouble Want more breaking political news? Click for the lat…