The omens did not bode well for “Kidnap,” a New Orleans-set action movie in which Halle Berry plays a single mother who stops at nothing to rescue her abducted 6-year-old son. Originally scheduled for a 2015 release and pushed back multiple times, the low-budget film has finally made its way into theaters – but in the doldrums of late summer (a traditional dumping ground for inferior product). Yet despite limited resources, a well-worn concept and a generic title, director Luis Prieto (“Pusher”) has managed to make a surprisingly effective thriller, leveraging the performance of his Oscar-winning star to convert an apparent junker into a lean, mean suspense machine. The minimalist plot is set into motion when Carla (Berry) takes her son (Sage Correa) to a crowded playground, taking her eyes off him for one moment to handle a phone call about the impending custody battle with her ex-husband, the boy’s father.