Fixed histograms in the CombinedChain ATR-22652
Fixed the issue with empty histograms reported by @dzanzi here: https://its.cern.ch/jira/browse/ATR-22652?focusedCommentId=3775863&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-3775863