Fixed #15912 -- Ensured that `forms.CharField.widget_attrs()` always returns a dictionary. Thanks to tsabi and rubyruy for the report and to mmcnickle and prestontimmons for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17096 bcc190cf-cafb-0310-a4f2-bffc1f526a37