“This is our first gig, so hold on—we’re just learning how to do this.” Last night at Bob Mould’s Bowery Ballroom show in New York, Ryan Adams came onstage to join Mould for an encore filled with Hüsker Dü songs. According to jambands.com, the songs included “I Apologize,” “Celebrated Summer,” “Something I Learned Today,” and “New…