[php-src] PR #24987: Fix GH-24802: guard request_parse_body() against reentrancy

Pull Request: https://github.com/php/php-src/pull/24987 Author: lazerg request_parse_body() has no reentrancy guard. If a user error handler that fires during multipart parsing calls it again, the nested parse re-inits and destroys the process-global PG(rfc1867_protected_variables). The outer parse then uses and frees that same table a second time, so the worker crashes on a bad zend_string_release(). The function already keeps its state in SG(request_parse_body_context), so I added an in_progress flag there. A reentrant call now throws RequestParseBodyException instead of parsing again, and the flag is cleared on exit and at the per-request reset points. Fixes #24802