Brian Peck wasn’t just a dialogue coach to child actors on Nickelodeon’s “All That” in the late ’90s and 2000s. Show stars Giovonnie Samuels and Bryan Hearne, who both joined the sketch-comedy production as preteens during its seventh season in 2002, actually considered Peck, then age 42, a friend. “We were extremely close,” Samuels, now...