Gregory Brown could have easily turned down the call about Bob Lanier. It has been only five weeks since the death of Brown’s wife, Yvonne, and he offers a description of love at first sight, in remembering her, that he draws from some favorite lines in Mario Puzo’s “The Godfather.” She was a thunderbolt in his life, beginning in the instant he saw her in a Black dance workshop at the University at Buffalo, more than 50 years ago. Yet losing Yvonne, and a promise made in her memory, has something to do with why Brown picked up the phone. Not long ago, he was in line at a Porter…