fix: handle empty host in relay AddrFeature ParseFrom for bind addresses

When rtcp listener calls Router.Bind with ":8000" (port-only address),
the relay AddrFeature.ParseFrom fails because net.SplitHostPort returns
an empty host. This leaves AType at default 0, causing AddrFeature.Encode
to return ErrBadAddrType.

Fix by normalizing port-only addresses to "0.0.0.0:<port>" in both tunnel
and relay connectors before ParseFrom. Also fix error check on
resp.WriteTo in the tunnel handler's handleBind to prevent silent
protocol desync.

handler/tunnel/bind.go

@@ -57,9 +57,12 @@ func (h *tunnelHandler) handleBind(ctx context.Context, conn net.Conn, network,
 			ID: connectorID,
 		},
 	)
-	resp.WriteTo(conn)
+	if _, err = resp.WriteTo(conn); err != nil {
+			log.Error(err)
+			return
+		}
 
-	// Upgrade connection to multiplex session.
+		// Upgrade connection to multiplex session.
 	session, err := mux.ClientSession(conn, h.md.muxCfg)
 	if err != nil {
 		return