Owen Gleiberman Chief Film Critic In “Spinning Gold,” a sketchy but adoring if not outright devotional biopic about Neil Bogart, the upstart ’70s music-industry mogul who founded Casablanca Records, there’s a pivotal moment that spins around the story of how Bogart, at a party he was throwing, played the 3-minute-and-20-second single version of Donna Summer’s “Love to Love You Baby.” He played it over and over again because his guests kept asking for it. That’s when the lightbulb went on. Bogart realized that the song needed to be longer, much longer — long enough to have sex to. (It ended up being 16 minutes and 50 seconds.) This is a rather famous anecdote (in the new documentary “Love to Love You, Donna Summer,” which just premiered at SXSW, there’s a clip of Bogart telling it on a talk show). So we assume that we’re going to see Bogart meet with Giorgio Moroder, the song’s composer and producer, and change music history.