_dbus_listen_tcp_socket: avoid leaking listen_fd in unlikely circumstances

_dbus_listen_tcp_socket: avoid leaking listen_fd in unlikely circumstances

If getaddrinfo (with port == 0) succeeds, the kernel gives us a port when
we first listen on a socket, we jump back to redo_lookup_with_port,
and getaddrinfo (with the nonzero port) fails, we leak listen_fd and all
the fds in it.

From the department of "without static analysis we'd never have spotted
this", or possibly "backward goto considered harmful".

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=29881
Bug-NB: NB#180486 CID-2389
Reviewed-by: Will Thompson <will.thompson@collabora.co.uk>