Strictly speaking, it's a proper noun, used to name the dog in question and so is entirely different in meaning and usage to the term used to insult people. For example, if the film were to be translated into (say) German, the proper nouns would probably remain intact, for example, "John", "Lancaster", etc. Conversely, nouns would in all likelihood be translated into their German equivalent, so instead of using the "N" word to insult someone, the German equivalent (if any) would be used instead. As such, I don't believe the dog's name can legitimately be lumped into the same category as the insult, however, while I can appreciate the difference, I suspect that C4 has to consider that some people will, given the opportunity, choose to actively take offence.