Reviewed by Geoff Garen.

r55878 changed UStringImpl::empty()->characters() to be non-null,
so TextBreakIteratorQt.cpp now should check the length of strings
(previously was assuming all strings with a non-null data pointer
had a length of at least 1).

* platform/text/qt/TextBreakIteratorQt.cpp:
(WebCore::wordBreakIterator):
(WebCore::characterBreakIterator):
(WebCore::lineBreakIterator):
(WebCore::sentenceBreakIterator):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@55934 268f45cc-cd09-0410-ab3c-d52691b4dbfc