Divide by zero error when getting offset of ZST

[adamchalmers]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

rust version

1.72.1

winnow version

0.5.16

Minimal reproducible code

use winnow::{prelude::*, token::any};

fn main() {
    let tokens = [Token];

    let result = my_parser.parse(&mut tokens.as_slice());
    let err = result.unwrap_err();
    let stream = err.input();

    let _offset = &stream[err.offset()];
}

/* The stream is a vec of custom tokens. */
type TokenSlice<'slice, 'input> = &'slice mut &'input [Token];

#[derive(Debug, Clone)]
pub struct Token;

pub fn my_parser(i: TokenSlice) -> PResult<()> {
    any.verify(|_| false).parse_next(i)?;
    Ok(())
}

Steps to reproduce the bug with the above code

cargo run

Actual Behaviour

thread 'main' panicked at /Users/adamchalmers/.cargo/registry/src/index.crates.io-6f17d22bba15001f/winnow-0.5.16/src/stream/mod.rs:1306:9:
attempt to divide by zero

Expected Behaviour

Report the correct offset (in this case, index 0)

Additional Context

Zero-sized types are a weird edge case and I don't expect this to actually come up. I found this bug while trying to minimize my reproduction for #341. I'd personally consider this a low-priority bug.