EtaJES and GNNC fix for high-pt jets

This MR fixes the behavior of the JES calibration for high pT jets. Previously, jets outside the range defined in the histogram with the spline correction factors would use the overflow bin value, which was 0, and this has been changed to use the same correction as the highest pT bin.

Tagging @lginabat who noticed this issue, as well as the conveners @mswiatlo @camacho @dportill @mspalla @dmelini @tpoulsen. @lginabat has tested this change, and confirmed that this fixes the problem.