Parties and protests don’t typically overlap, but the “Selma” cast made an exception and a statement on Sunday night following the film’s Manhattan premiere. At one point during the otherwise splashy festivities, director Ava DuVernay took to the steps of the New York Public Library with actors David Oyelowo, E. Roger Mitchell, Wendell Pierce, Omar Dorsey, John Lavelle, Stephan James, Kent Faulcon, Lorraine Toussaint, Andre Holland, Tessa Thompson and Colman Domingo, donning “I Can’t Breathe” T-shirts over their partywear and raising their arms in the “don’t shoot” pose. It was not just an unusually sobering photo op, but also a...