merge from trunk r49214

fix FillRandom(hist) for case of histograms with different axis, 
see https://sft.its.cern.ch/jira/browse/ROOT-4938


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@49216 27541ba8-7e3a-0410-8455-c3a389f83636