BUG: wrong bounding of sensitivity contituents in case of many control boxes

Summary

When more than one volumetric B-Splines control boxes are present, the sensitivity constituents corresponding to the non-active design variables are not bounded(zeroed) correctly. The resultant sensitivities, used in the optimization, are bounded correctly, so this is more a bug pertaining to the output file of the sensitivities rather than a functional one.

Things work as intended in the presence of a single volumetric B-Splines control box.