LArADC2MeVCondAlg: Do not consider missing Ramps for Barrel Presampler in LOW gain a problem
As discussed in ATLASRECTS-7560, for some older runs the conditions database contains no ramps for the barrel presampler in low gain. This is not a real problem, the presampler is never in low gain. This MR makes the LArADC2MeVCondAlg more robust in this situation.