This was causing a crash in one of the MARI scripts due to a spectrum
without any detectors not being masked in a call to ConvertUnits
Also tighten up unit tests on the validations applied on various units
GetAllEi wasn't supplying an L2 value when doing an energy unit conversion
because it stuffs L_tot into the L1 field. Have supplied an L2 value of 0
here to avoid the new validation logic on the Energy unit