fixed possible NPE

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@9755 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
only set appendTo if != null

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@9756 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c