PARIS—Former champion Garbine Muguruza suffered a second consecutive first-round exit at the French Open, biting the red dirt in a 2–6 6–3 6–4 loss to Estonian Kaia Kanepi on Sunday as she continued on her downward trend. Muguruza, who lifted the Suzanne Lenglen Cup in 2016 and reached the semifinals at Roland Garros two years…