Rihanna Stalker -- Deemed 'Credible Threat,' Spends 277 Days in Jail

A man convicted of stalking Rihanna spent 277 days behind bars after showing up at her L.A. home and scaring the crap out of the singer ... and now he's out and living in the same city as Rihanna ...TMZ has learned. Zentil Vanzellas was convicted of…