Harmless as a puppy, “Bolt” comes bounding into theaters, stumbling over its big, goofy paws, wagging its fluffy tail and begging to play ball. It’s sweet and eager to please but, sadly, nothing terribly special: Girl finds dog, girl loses dog, girl gets dog back. You’ve seen this sort of thing many times before, namely in any movie with the word “Lassie” in the title.