Pull request for Issue811: AM1DCalibrationABEditor crash bug

Fixed up a missing null initialization for chooseScanDialog_ (which later had a null check) and changed the range of energyCalibrationReferenceBox_ from 1000 to 20,000

This may need testing on a another beamline. Not sure where abouts I would go to on SGM to find this (nor even if its used on here)