fixed bug in logLik.loglm with zero frequencies

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/vcdextra@228 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
fixed bug in logLik.loglm with zero frequencies

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/vcdextra@229 edb9625f-4e0d-4859-8d74-9fd3b1da38cb