The extras on “Finding Neverland” only truly soar when Johnny Depp shows his playful side. In blooper after blooper, he cracks up co-stars and crew with flubs and fart machines. But when the cameras roll for puffy behind-the-scenes featurettes, he speaks glowingly of the same, yet barely cracks a smile. The pic’s commentary track with helmer Marc Forster, scribe David Magee and producer Richard N. Gladstein is also terminally polite; it, too, could also use some of the whimsy “Peter Pan” scribe J.M. Barrie fosters onscreen.