Wrong while_let_on_iterator suggestion

[jsgf]

In this code:

pub fn arg_value<'a>(
    args: impl IntoIterator<Item = &'a String>,
    find_arg: &str,
    pred: impl Fn(&str) -> bool,
) -> Option<&'a str> {
    let mut args = args.into_iter().map(String::as_str);

    while let Some(arg) = args.next() {
        let arg: Vec<_> = arg.splitn(2, '=').collect();
        if arg.get(0) != Some(&find_arg) {
            continue;
        }

        let value = arg.get(1).cloned().or_else(|| args.next());
        if value.as_ref().map(|p| pred(p)).unwrap_or(false) {
            return value;
        }
    }
    None
}

Clippy warns:

warning: this loop could be written as a `for` loop
  --> src/lib.rs:10:27
   |
10 |     while let Some(arg) = args.next() {
   |                           ^^^^^^^^^^^ help: try: `for arg in args { .. }`
   |
   = note: #[warn(clippy::while_let_on_iterator)] on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#while_let_on_iterator

However this is wrong because args.next() is called again within the body of the loop. Applying this suggestion would not compile.

Clippy gets this right in a simpler case, but I haven't tried to minimize this test case further.

This repos in current stable and nightly clippy:
clippy 0.0.212 (b2601be 2018-11-27)
clippy 0.0.212 (1b89724 2019-01-15)

[jsgf]

I'm not sure if this is a dup of #1033