ATLANTA — Martin Prado and Justin Bour each had an RBI double in the eighth inning and the Miami Marlins extended Shelby Miller’s winless streak to 19 starts with a 4-0 victory over the Atlanta Braves on Monday night. Miller, an All-Star with a sparkling 2.56 ERA, began the night with the worst support in the majors, and the Braves, losers in six straight and 13 of 14, stayed true to form. Beginning the night with the worst average (.227) in the NL with runners in scoring position since the All-Star break, Atlanta has scored two runs or less in 20 of Miller’s 27 starts.