pmchart: (coverity) check return value from pmConvScale()
pmchart: (coverity) check return value from pmConvScale()

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp