String::replace_range leads to runtime errors while it should not

[Anatoly03]

🐛 Bug description

String::replace_range(&mut self) leads to RuntimeError: unreachable

🤔 Expected Behavior

The range should be replaced without assertions

👟 Steps to reproduce/ MRE

use wasm_bindgen::prelude::*;

use super::filter::Filter;

#[wasm_bindgen]
impl Filter {
    pub fn replace(&mut self, content: String) -> String {
        let mut censored = // String Content
        let ranges = ... // Vector of Ranges

        for range in ranges {
            censored.replace_range(range, "*");
        }

        censored
    }
}

🌍 Your environment

Intel Mac
wasm-pack and rustc version: