Bob GarverSpecial to the Valley NewsSince Po (Jack Black), the main character of the “Kung Fu Panda” movies, is known for his corpulent eating habits, it makes sense to compare the animated franchise to a sort of comfort food. These movies aren’t exactly “healthy” choices that send the imagination soaring, but they aren’t “junk” that people outside the target audience are likely to detest. They’re agreeable, but not spectacular. Fortunately for “Kung Fu Panda 4,” it’s arriving at a time when kids haven’t had a decent movie for a while. Even though it coasts on preexisting goodwill at times, it’s not the painful, phoned-in effort it could have been.At the start of the movie, Po is basking in his fame as the legendary Dragon Warrior. He does his job we
