while_let_on_iterator false positive with nested loop

[sinkuu]

fn main() {
    let mut it = 1..100;

    for _ in 0..10 { // or any other loop
        while let Some(x) = it.next() { // (false positive) this loop could be written as a `for` loop
        }
    }
}

while_let_on_iterator lint should ignore a while let Some(x) = iterator_variable_external_to_loop within a loop, because iterators cannot be consumed there.

[sinkuu]

Duplication of https://github.com/Manishearth/rust-clippy/issues/600