Merge branch 'feature/8443_many_singletons' into feature/8455_correct_sample_geom_cor
re #8455: SampleGeomCor uses only public methods from isis_reducer

Code improvement. It does not use the protected attribute _sample_run,
but only public methods. Besides, it does not calculate twice the same
value for volume, using the value calculated already.
Merge remote-tracking branch 'origin/feature/8455_correct_sample_geom_cor'