GM Korea CEO Hector Villarreal, right, poses with Wi Ha-joon, the ambassador of the premium auto brand, as they showcase Buick's Electra E7 plug-in hybrid SUV during the vehicle's launch event in Seoul, Wednesday. YonhapGeneral Motors (GM) Korea launched its premium auto brand Buick at an event in Seoul on Wednesday, signaling a stronger commitment to the Korean market amid persistent speculation over the carmaker's possible withdrawal from the country.The launch brings to four the number of brands GM Korea operates in Korea — Chevrolet, Cadillac, GMC and Buick — as the automaker seeks to broaden its customer base. Buick’s…