SAN FRANCISCO — The Giants were headed for an outfield shakeup at some point after a slow start, but Wednesday’s roster moves came because of injuries, not ineffectiveness. Starting center fielder Harrison Bader was put on the IL with a left hamstring strain and backup Jared Oliva joined him with a left wrist hamate fracture. To fill the roster spots, the Giants recalled Triple-A outfielders Will Brennan and Drew Gilbert. Bader originally strained the hamstring at the end of camp, but he recovered in time to make the Opening Day roster. So far, however, there hasn’t been much production from the offseason addition. Bader is hitting just .115 with a .338 OPS over the first month of a two-year deal. Oliva started in center on Tuesday and is 1-for-7 in seven appearances. He made the roster after a big spring and the Giants hoped he would get a chance to pinch-run just about every game, but their offense has been so bad early on that there haven’t been many opportunities. Hamate surgery often saps a hitter’s power for months after he returns, but Oliva’s game is built on speed and defense so the recovery should be a bit more...