Fixed compilation with Geant4 10.5

Hi, Could you, please, merge the fixes in this PR? I am preparing a new Geant4 VMC version, which will be based on ROOT 6.14/06 and Geant4 10.5. Would it be possible to make a new tag when these fixes are included, so that we can refer to this tag in the Geant4 VMC tag? I am also getting the following debug messages from VMC/Garfield example: TrackHeed::UpdateBoundingBox: Center of bounding box: x: 0 cm y: 0 cm z: 0 cm While we did not get them with previous version. Could this be also cleaned-up? Thank you, Ivana