The Guild of Music Supervisors proved not too white with such fare as “Straight Outta Compton,” “Empire” and “Bessie” — all chronicling the African-American experience through music — claiming top honors Thursday night at the Theater at Ace Hotel in downtown Los Angeles. The sixth annual affair, each more widely attended than the last — the Ace’s reconstituted ’20s-era gothic movie palace being its most lavish venue yet — represented another display of camaraderie between thi