[php-src] PR #24177: Fix leak when the added previous exception is already in the chain

Pull Request: https://github.com/php/php-src/pull/24177 Author: EdmondDantes zend_exception_set_previous() takes ownership of add_previous: every exit either releases it or stores it as previous. When the walk over the exception's previous chain reaches add_previous itself, the loop ends and the function returns without releasing it. Pure PHP reaches it from finally: ```php function f() { $e = new RuntimeException("x"); try { throw $e; } finally { throw new LogicException("y", 0, $e); } } try { f(); } catch (Throwable $t) {} ``` A debug build reports Freeing ... (152 bytes), Total 1 memory leaks detected on PHP-8.4 and master. The fix releases add_previous after the loop, as the other discarding exit does. Test: Zend/tests/try/try_finally_previous_already_in_chain.phpt, with the pending exception as the direct previous and one level deeper.