Fixes <http://bugzilla.opendarwin.org/show_bug.cgi?id=3359> Crash on hover with certain styles on the text applied

        If a zero length render object (such as a text node that has been set to "") occured at the
        end of a line, it was previously given a non-zero sized run.  Iteration over such a node would cause
        a crash.

        Test cases added:
        * layout-tests/traversal/size-zero-run-expected.txt: Added.
        * layout-tests/traversal/size-zero-run.html: Added.

        * khtml/rendering/bidi.cpp:
        (khtml::appendRun):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@9989 268f45cc-cd09-0410-ab3c-d52691b4dbfc