Bug in `string/aho_corasick` algorithm

[guopenghui]

Rust/src/string/aho_corasick.rs

Line 80 in a5cf37c

ans.push(&s[i - len + 1..=i]);

It will cause computing overflow when pattern appear at head of string.

If i - len + 1 == 0, i - len will be -1 first, then panic.

Change to i + 1 - len will solve this.

[siriak]

Thanks for reporting, could you make a PR with the proposed changes?

[github-actions]

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