<rdar://problem/4244976> reproducible hang at ocharleys.com in VisiblePosition::initDownstream

        Problem is that RenderText::nextOffset() passes an empty string the UBreakIterator, which returns
        UBRK_DONE (-1) from ubrk_following, and that -1 is used without question as return result of
        nextOffset().  Fixed by checking for UBRK_DONE and returning offset+1 in that case.  Similar
        change in RenderText::previousOffset().

        Test cases added:
        * layout-tests/editing/selection/extend-by-word-002-expected.checksum: Added.
        * layout-tests/editing/selection/extend-by-word-002-expected.png: Added.
        * layout-tests/editing/selection/extend-by-word-002-expected.txt: Added.
        * layout-tests/editing/selection/extend-by-word-002.html: Added.

        * khtml/rendering/render_block.cpp:
        (khtml::RenderBlock::updateFirstLetter):
        Added comments.  Slight format adjustments.

        * khtml/rendering/render_text.cpp:
        (getCharacterBreakIterator):
        Slight format adjustment.

        (RenderText::previousOffset):
        (RenderText::nextOffset):
        Check for UBRK_DONE.

        (RenderTextFragment::RenderTextFragment)
        (RenderTextFragment::RenderTextFragment)
        Fixed parameter names.

        (m_generatedContentStr):
        * khtml/rendering/render_text.h:
        Fixed parameter names in the two RenderTextFragment constructors.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@10541 268f45cc-cd09-0410-ab3c-d52691b4dbfc