Gottfried Huppertz’s score for “Die Nibelungen,” which spent decades in states of neglect, is not the most breathtaking music; it’s likely that no one would rank it above Wagner’s operas. But it is impressive, sometimes infectious, in its own way. And Huppertz’s writing is so tightly entwined with the storytelling onscreen, giving each scene its very heartbeat, that it’s hard to imagine the future of Hollywood’s great soundtracks without him.