Fixed #15018 -- Corrected the handling of LimitedStream under one edge case...

Fixed #15018 -- Corrected the handling of LimitedStream under one edge case involving size restricted buffers and newlines. Thanks to xjdrew for the report, and aaugustin for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15222 bcc190cf-cafb-0310-a4f2-bffc1f526a37