The key moment in “Justin Bieber’s Believe,” the new hagiographical film, comes in the second half, in a segment that touches ever so lightly upon Mr. Bieber’s tumultuous public image over the last year. The scene is London, last March: A small cluster of paparazzi is egging Mr. Bieber on, and he takes the bait, jumping at the photographers and being held back by a bodyguard. At least half of the conversation (on both sides) is bleeped. ....... 