Jennifer Garner was spotted in Los Angeles ready to celebrate an early birthday party in the midst of ex-husbandBen Affleck and Jennifer Lopez’s recent engagement announcement. The 13 Going On 30 actress is getting ready to turn 50! She was seen carrying her own birthday cake while exiting her car in Los Angeles. The star of Netflix’s latest The Adam’s Project was snapped wearing a loose-fitting black sweater and blue jeans with her hair up in a bun. The mother of three let her hair down by the time she left the event. Garner’s outing came days after J. Lo’s announcement that she was engaged t…