slug length counter bumps slug over max_length limit

When creating multiple videos with the same title, the unique counter appended to the slug bumps the entire thing over the max_length of 50 chars. related to #249
I've been wondering if we'd want to make one query to the database versus multiple queries, which is why I was thinking about using the method I mentioned here https://github.com/willkg/richard/issues/249#issuecomment-49618616