needless_range_loop suggests using iter on a value that do not have iter method

In this example:

``` rust
use std::ops::Index;

struct S(Vec<u32>);

impl Index<usize> for S {
    type Output = u32;

    fn index(&self, index: usize) -> &u32 {
        &self.0[index]
    }
}

fn main() {
    let s = S(vec![1, 2, 3]);

    for i in 0..3 {
        println!("{:?}", s[i]);
    }
}
```

Clippy says "Consider using `for item in s.iter().take(3)`, but `s` does not have `iter` method.
