“Night Swim” (*1/2 out of four) was a shallow dud that drowns in its own horror-movie cliches about a family (Wyatt Russell, Kerry Condon, and others) who become terrorized by an evil spirit in their swimming pool and as a result their home. A 15-minute idea padded out to feature length with hardly any scares and even less originality. It’s no surprise that this was originally based on a 2014 short film and short is what it should have stayed.