Incorrect suggestion by `useless_let_if_seq` lint

Hi,

Given the following code:

fn test(idx: usize) -> bool {
    idx % 2 == 0
}

fn algo(mut x: usize, y: usize, height: usize, width: usize) {
    let mut last_row_length = 0;
    let mut sx = x;

    if last_row_length != 0 && test(y * width + x) {
        loop {
            last_row_length -= 1;
            if last_row_length == 0 {
                return;
            }
            x += 1;
            if !test(y * width + x) {
                break;
            }
        }
        sx = x;
    } else {
        while x != 0 && !test(y * width + x - 1) {
            x -= 1;

            if y != 0 && !test((y - 1) * width + x) {
                algo(x, y - 1, width, height);
            }

            last_row_length += 1;
        }
    }
    
    println!("{}", sx);
}

clippy suggests the following:

warning: `if _ { .. } else { .. }` is an expression
  --> src/main.rs:7:5
   |
7  | /     let mut sx = x;
8  | |
9  | |     if last_row_length != 0 && test(y * width + x) {
10 | |         loop {
...  |
30 | |         }
31 | |     }
   | |_____^ help: it is more idiomatic to write: `let <mut> sx = if last_row_length != 0 && test(y * width + x) { ..; x } else { ..; x };`
   |
   = note: #[warn(useless_let_if_seq)] on by default
   = note: you might not need `mut` at all
   = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.212/index.html#useless_let_if_seq

This is incorrect, since x is modified in the loop in the else path, but NOT assigned to sx.

(Playground link)

(Note: the code itself is not the most idiomatic, since I'm transcribing an algorithm from another language...)

Reproduce the diagnostic using the src/main.rs example and the linked Playground, then start from the useless_let_if_seq lint entry point. Check the suggested transformation against the differing x and sx values in both branches; it is done when the lint no longer proposes a transformation that changes the program's result.