ZOMBIES are a value stock. They are wordless and oozing and brain dead, but they’re an ever-expanding market with no glass ceiling. Zombies are a target-rich environment, literally and figuratively. The more you fill them with bullets, the more interesting they become. Roughly 5.3 million people watched the first episode of “The Walking Dead” on AMC, a stunning 83 percent more than the 2.9 million who watched the Season 4 premiere of “Mad Men.” This means there are at least 2.4 million cable-ready Americans who might prefer watching Christina Hendricks if she were an animated corpse.