Sometimes a film contains a single scene that feels like its main reason for being. In Sonejuhi Sinha’s grimy-glamorous crime thriller feature debut “Stray Dolls,” it comes late on: Riz (Geetanjali Thapa), a newly arrived undocumented immigrant from India who is working as a maid in a dead-end motel, is in a phone booth at night talking to her mom back home.