ElectronCombinedMaterialEffects : Avoid repeated divisions. div are typically more expensive that mult see [https://indico.cern.ch/event/252634/contributions/564148/attachments/440055/610507/2013-06-10-swtut.pdf] slide 3
this should prb change output at the following (0.00000183%) level
009.GSFTrackParticlesAuxDyn.trackParameterCovarianceMatrices.18.35 1.2134378835071402e-08 -> 1.2134377946892982e-08 => diff= [0.00000183%]