The previous implementation allowed for high surrogates followed by
non-low surrogates. We now assure that every high surrogate is followed
by a low surrogate (under the assumption that the last byte in an XMPP
stream can not be a unicode surrogate pair).

OF-391

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/trunk@13996 b35dd754-fafc-0310-a699-88a17e54d16e