utp close-reason use after free fix

ChangeLog

@@ -1,3 +1,4 @@
+	* utp close-reason fix
 	* exposed default add_torrent_params flags to python bindings
 	* fix redundant flushes of partfile metadata
 	* add option to ignore min-interval from trackers on force-reannounce

src/utp_stream.cpp

@@ -1513,7 +1513,7 @@ void utp_socket_impl::parse_close_reason(boost::uint8_t const* ptr, int size)
 	UTP_LOGV("%8p: incoming close_reason: %d\n"
 		, static_cast<void*>(this), int(incoming_close_reason));
 
-	if (m_userdata == 0) return;
+	if (m_userdata == 0 || !m_attached) return;
 
 	utp_stream::on_close_reason(m_userdata, incoming_close_reason);
 }