Fernando Tatis Jr. has now allowed more home runs than he’s tallied. The slumping Padres outfielder’s miserable season continued Friday night when his error led to a Little League grand slam for the Cardinals’ JJ Wetherhold in San Diego’s 6-0 home loss. Tatis’ error turned what should have at most a two-run single into a single that cleared the bases and gave the Cardinals a 4-0 lead in the fifth inning. The two-time Gold-Glove winning right fielder simply whiffed while running forward, with the ball going completely under his glove and rolling all the way to the right field wall. Wetherhold didn’t even have to slide to notch his four-bagger. “He’s a playmaker, just trying to make a play,” Padres manager Craig Stammen said, per MLB.com . “He just came up short.” Tatis is normally a surefire defender, with two Gold Gloves in the last three years, including last season, and it’s possible his struggles at the plate are starting to weigh on him. Fernando Tatis Jr.…