A 24-week, Multicentre, Randomised, Double-Blind, Placebo-Controlled, Parallel-Group, International Phase III Study With 24 Week Extension to Evaluate the Safety and Efficacy of Dapagliflozin 10 mg/Day in Patients With Type 2 Diabetes Who Have Inadequate Glycemic Control on a DPP-4 Inhibitor Sitagliptin+/-Metformin