#i123862# use O*String's isEmpty() method to check for emptiness in chart2 module

Patch-by: j.nitschke@ok.de
Review-by: hdu@apache.org


git-svn-id: https://svn.apache.org/repos/asf/openoffice/trunk@1566533 13f79535-47bb-0310-9956-ffa450edef68