Fixes the warning in incrementalApplyExtraAdditionalFormats being
triggered when the document is reduced in size while a highlight is
running.

Change-Id: I60e0c8772d511f52ee433d27cc77ba726030b354
Reviewed-on: http://codereview.qt-project.org/4661


Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>