webrtcbin: connection is not established without remote candidates (even when they are not needed)

If add-ice-candidate is not called, connection will not be established. However, if running with public IP address (on a server) it is not needed.

As a proof, this nonsense is sufficient to trick GStreamer into not requiring real proper candidates and establish connection successfully:

webrtcbin
    .emit(
        "add-ice-candidate",
        &[&0u32, &"candidate:0 1 udp 0 0.0.0.0 0 typ host".to_string()]
    )
    .unwrap();

Would be nice to remove the need for such a hack entirely.