when checking if two histogram have both labels skip case when one of the histogram is empty
when checking if two histogram have both labels skip case when one of the histogram is empty


git-svn-id: acec3fd5b7ea1eb9e79d6329d318e8118ee2e14f@44770 27541ba8-7e3a-0410-8455-c3a389f83636

bbockelm/root-historical,bbockelm/root-historical,bbockelm/root-historical,bbockelm/root-historical,bbockelm/root-historical,bbockelm/root-historical,bbockelm/root-historical