`BoundedBacktracker::is_match` panics on empty haystack when `max_haystack_len()` saturates to 0

[Stranger6667]

What version of regex are you using?

regex-automata 0.4.14

Describe the bug at a high level.

Panic in BoundedBacktracker::is_match while I'd expect an Err during regex construction time (despite the large size limit). Appeared in the jsonschema crate when I tried to compile all regular expressions I mined from the Open API directory repo.

What are the steps to reproduce the behavior?

use regex_automata::meta::Regex;

let cfg = Regex::config().nfa_size_limit(Some(1_000_000_000));
let re = Regex::builder().configure(cfg).build(r"^.{0,404600}$").unwrap();
re.is_match("");  // panics

What is the actual behavior?

Panic:

thread 'main' panicked at regex-automata-0.4.14/src/meta/wrappers.rs:234:68:
called `Result::unwrap()` on an `Err` value: MatchError(HaystackTooLong { len: 0 })

What is the expected behavior?

I'd expect either a build-time error (like the existing CompiledTooBig for this shape, see #802) or a clean runtime Err - but not a panic:

Regex::builder().configure(cfg).build(r"^.{0,404600}$")

Additionally, HaystackTooLong with len: 0 reads weird as I'd expect some large value there instead of 0 (implied by the TooLong part of the enum variant name).