Midway through Florence + the Machine’s headlining set at the BottleRock Napa Valley festival on Saturday, the audience exploded in a spontaneous chant: Warriors! Florence Welch, the British band’s siren-voiced singer and namesake, may not have realized that the Golden State Warriors just scored a season-saving win over the Oklahoma City Thunder in Game 6 of the NBA Western Conference finals, but the unexpected triumph certainly energized an already enthusiastic crowd of about 40,000 fans across the Napa Valley Expo.