Fix empty IDs for redirects & tracked 404 errors

[eminos]

Summary

• falls back to a deterministic hash-based ID when a tracked 404 URL cannot be slugged
• keeps existing slug-based IDs for normal URLs
• adds regression coverage for malformed URLs like /)

Fixes #558.

Testing

• ./vendor/bin/phpunit tests/Redirects/Stache/ErrorRepositoryTest.php tests/Redirects/RecordErrorTest.php
• ./vendor/bin/pint --test src/Redirects/Stache/ErrorRepository.php tests/Redirects/Stache/ErrorRepositoryTest.php

[duncanmcclean]

Thanks! I wonder if we might need to do this in the RedirectRepository too 🤔

(I'm on it)

[eminos]

I have no clue Duncan. I stumbled upon this issue on a production site and let Codex investigate, and it came up with this.
Sorry if it's not a perfect PR. I'm thinking better a "90%" PR than no PR at all 🙂
But just let me know if you rather not have these Codex (5.5) generated PRs.

[duncanmcclean]

No worries.

Taking a look now - will merge & tag shortly. Thanks for the pull request!