Fix vtkPlotBar::GetBounds logic when log scale is enabled

- address paraview/paraview#22733
- This commit fixes the logic in the
  `vtkPlotBar::GetBounds(double*, bool unscaled)` method
  to scale the bounds only if `unscaled` is false. Previously,
  it returned unscaled bounds even when `unscaled` was false and
  returned scaled bounds when `unscaled` was true.