The second season of the “Walking Dead” spinoff “Fear the Walking Dead” premiered Sunday on AMC to huge ratings. It was the most-watched thing on Sunday on cable and broadcast. But taking a step back, it’s a good time to appreciate just what the “Walking Dead” franchise has done for the two companies that distribute it, AMC Networks on television and Image Comics in print.Namely, say what you will about the show or the comic book, but it’s managed to fund a creative renaissance at two of the top producers of original content in their respective mediums.That “The Walking Dead” is the top show on cable isn’t exactly news.