fix some invariant check failures in metadata transfer edge cases

src/bt_peer_connection.cpp

@@ -1617,6 +1617,7 @@ namespace libtorrent
 		if (extended_id == 0)
 		{
 			on_extended_handshake();
+			disconnect_if_redundant();
 			return;
 		}
 

src/peer_connection.cpp

@@ -829,6 +829,9 @@ namespace libtorrent
 		on_metadata();
 		if (m_disconnecting) return;
 
+		disconnect_if_redundant();
+		if (m_disconnecting) return;
+
 		// let the torrent know which pieces the
 		// peer has
 		// if we're a seed, we don't keep track of piece availability