After premiering at Sundance and screening at Cannes earlier this year, writer-director Pippa Bianco's searing drama Share debuts on HBO this Saturday night, and it's one of the cabler's best acquisitions in years. The film, which is based on Bianco's 2015 short of the same name, was produced by A24, and yet that indie distributor put it up for sale, likely because it's extremely unlikely that Share's best-case-scenario box office haul would justify a theatrical release with a proper marketing budget, given its challenging subject matter and lack of stars. Instead, …