Repertoire rediscovery belongs to the Vienna Piano Trio's long list of cardinal virtues. The ensemble introduced Wigmore Hall audiences to the teenage Leonard Bernstein’s Piano Trio at the end of last season. It returns with the astonishingly sumptuous arrangement of Verklärte Nacht, penned for piano trio by Schoenberg’s pupil Eduard Steuermann 80 years ago but not publicly performed until after its belated appearance in print in 1979.