This isn’t the first time that Thao Nguyen has sold out the Black Cat. It’s actually become an expectation, like death and taxes, that the young guitarist from Falls Church, VA and her awkwardly named band will bring the crowds and start a party. Party seems an unlikely description of a show by a band who specializes in rather harsh tunes about heartbreak and loss. But Thao’s feisty presence and quickness to invite others onstage…