StreamExt::buffered and StreamExt::buffer_unordered hangs for n = 0

[EFanZh]

Try the following code:

use futures::executor;
use futures::stream::{self, StreamExt};
use std::future;

fn main() {
    executor::block_on(async {
        let mut s = stream::iter(0..10).map(future::ready).buffered(0);

        while let Some(value) = s.next().await {
            println!("{}", value);
        }
    });
}

Is this the expected behavior?

[taiki-e]

I feel this is a bug. I think it's preferable to panic if capacity is 0, like chunks.

futures-rs/futures-util/src/stream/stream/chunks.rs

Line 26 in e981716

assert!(capacity > 0);