Fix the egs_chamber region-specific ECUT check
Fix the egs_chamber region-specific ECUT check

Fix the ECUT check in egs_chamber that is used when a user selects the
ECUT regions specifically in their calculation geometry. The bug was
that the rest mass was subtracted from the particle energy during the
ECUT comparison, effectively resulting in the ECUT being 0.511 MeV
higher than it should have been. This has now been resolved.

mchamberland/EGSnrc,MartinMartinov/EGSnrc,MartinMartinov/EGSnrc,crcrewso/EGSnrc,MartinMartinov/EGSnrc,crcrewso/EGSnrc,nrc-cnrc/EGSnrc,mchamberland/EGSnrc,crcrewso/EGSnrc,nrc-cnrc/EGSnrc,MartinMartinov/EGSnrc,nrc-cnrc/EGSnrc,crcrewso/EGSnrc,mchamberland/EGSnrc,nrc-cnrc/EGSnrc,MartinMartinov/EGSnrc,mchamberland/EGSnrc,mchamberland/EGSnrc,crcrewso/EGSnrc,nrc-cnrc/EGSnrc,mchamberland/EGSnrc