`rustfmt` wrongly deletes labels

```rust
match x {
    0 => 'label: {
        if some_flag {
            break 'label;
        }
        println!("hello");
    }
    _ => { println!("no hello"); }
}
```

becomes

```rust
match x {
    0 => {
        if some_flag {
            break 'label;
        }
        println!("hello");
    }
    _ => { println!("no hello"); }
}
```

after formatting.