Mvd bugfix: use of an uninitialised array

fix use of an uninitialised array sigmaIn and shiftIn here: https://git.cbm.gsi.de/computing/cbmroot/-/blob/master/reco/detectors/mvd/plugins/tasks/CbmMvdSensorHitfinderTask.cxx?ref_type=heads#L493

The MR should fix the tracker timeout problem in the other MR: !1557 (comment 38110)