Improve let-chain indentation

[A4-Tacks]

Current formatted code:

fn too_long_function_name_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxcxxxxxxxxxxxxxxxxxxxx()
-> Option<i32> {
    None
}

fn main() {
    if let Some(x) =
        too_long_function_name_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxcxxxxxxxxxxxxxxxxxxxx()
        && x != 0
    {
        println!("x")
    }
}

If you don't pay attention to the = at the end of the previous line,
you may think that this call returns a bool

Expect improved formatted code:

fn too_long_function_name_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxcxxxxxxxxxxxxxxxxxxxx()
-> Option<i32> {
    None
}

fn main() {
    if let Some(x)
        = too_long_function_name_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxcxxxxxxxxxxxxxxxxxxxx()
        && x != 0
    {
        println!("x")
    }
}

or

fn too_long_function_name_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxcxxxxxxxxxxxxxxxxxxxx()
-> Option<i32> {
    None
}

fn main() {
    if let Some(x) =
            too_long_function_name_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxcxxxxxxxxxxxxxxxxxxxx()
        && x != 0
    {
        println!("x")
    }
}