magento/magento2#32599: Fix segfault when base URL config is empty

[swnsma]

Description (*)

Fixes infinite recursion (SIGSEGV / stack overflow) in store config placeholder processing when web/secure/base_url or web/unsecure/base_url is NULL or empty.

Magento\Store\Model\Config\Placeholder previously kept recursing on unresolved {{secure_base_url}} / {{unsecure_base_url}} placeholders. It now throws a clear, localizable LocalizedException instead.

Fixes #32599

Fixed Issues (if relevant)

1. Fixes NULL value for web/secure/base_url generates a SEGSERV error #32599 — NULL value for web/secure/base_url generates a SEGSERV error

Manual testing scenarios (*)

1. Set web/secure/base_url in core_config_data to NULL (ensure no higher-priority env override).
2. Flush caches.
3. Load storefront or run bin/magento.
4. Before: PHP-FPM child dies with SIGSEGV / max stack size error.
5. After: A clear exception: Cannot resolve "{{secure_base_url}}" because "web/secure/base_url" is empty.

Questions or comments

Unit and integration tests cover null/empty/missing base URL for both secure and unsecure placeholders, plus the scope-level Processor\Placeholder path.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md related to the contributed code is updated, included or not required
• All automated tests passed successfully (all builds are green) — pending CI

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[swnsma]

@magento run all tests