Fix panic in BoundedBacktracker when max_haystack_len returns 0

[VrtxOmega]

Fixes #1344

Problem

When a regex like ^.{0,404600}$ causes the bounded backtracker's max_haystack_len() to return 0, the meta layer's guard in wrappers.rs used '>' instead of '>=', allowing the engine to be selected for an empty string (length 0). The engine then panicked with MatchError(HaystackTooLong { len: 0 }) from an unwrap() at wrappers.rs:234.

Root Cause

In src/meta/wrappers.rs, BoundedBacktrackerEngine::get() guards against haystacks that are too long for the backtracker:

When max_haystack_len() returns 0, this guard evaluates to (false), so the engine IS selected. But the engine itself cannot handle any haystack (even length 0) and returns an error.

Fix

Changed the guard from '>' to '>=' so that when max_haystack_len() is 0, no haystack is selected for the backtracker engine:

Verification

• Reproduced the panic: built regex-automata 0.4.18, ran MCVE from issue, confirmed panic at wrappers.rs:234 with MatchError(HaystackTooLong { len: 0 })
• After fix: MCVE returns Ok(true) correctly (empty string matches ^.{0,404600}$)
• Added regression test max_haystack_len_zero_excludes_engine
• All existing tests pass: 2 passed, 0 failed