Dolly Parton thinks “you have to work at being happy”. The 78-year-old singer is well-known for her upbeat outlook, but Dolly admits that it still takes some “work”. The ‘9 to 5’ hitmaker told the Guardian newspaper: “You have to work at being happy. Some people work at being miserable. “If I wake up in the morning and don’t feel great or things are not great, I try to think about what I can do to make things work better, rather than just falling into that deep hole, because then you just go deeper and deeper. “I just try to have a good attitude and make things right; to be grateful for the th…