LArDigitContainerCnv_p2::persToTrans: Protect against empty input container
Fix segfaults observed in a few test. An empty input container led to a zero-divided-by-zero situation. This update protects against this. Closes ATLASRECTS-4973
Fix segfaults observed in a few test. An empty input container led to a zero-divided-by-zero situation. This update protects against this. Closes ATLASRECTS-4973