It was no laughing matter.“Stranger Things” star Jamie Campbell Bower, who plays lord of the “upside-down” Vecna in the Netflix series, has come a long way since he bombed his audition for the hero of the “Harry Potter” franchise — if only his penchant for naughty jokes hadn’t gotten the best of him.The 33-year-old actor revealed the blunder while appearing on Josh Horowitz’s “Happy Sad Confused” podcast.As Bower tells it, the young actor had a meeting with the film’s first director, Chris Columbus, for which he was asked to prepare a joke.“I had just heard this joke about a fairy,” recalled Bower. “Like, the reason why the fairy sits on top of the Christmas tree.