topic filter is_match appears to be wrong

[pabigot]

Why does this test pass?

#[test]
fn topic() {
    let t = mqtt::topic::TopicFilter::new("dmxlight/dmx1/+").unwrap();
    assert!(t.is_match("dmxlight/dmx1/btf1/set"));
}

Given that the trailing fragment btf1/set contains a delimiter so is not a single-level?

[fpagliughi]

Yeah, that's definitely wrong!