[php-src] PR #24435: Zend: always populate error pointer on failure of zend_is_callable()

Pull Request: https://github.com/php/php-src/pull/24435 Author: Girgias Most of the code base expects an error to be set if a char* is provided, as this used to be always the case. It no longer was the case since the partially supported callables were deprecates as the deprecation could be promoted to an exception in which case we skipped allocating a char*. The simple fix, allocate a char* even in case of an exception so callers don't need to check if it still NULL. This fixes some error messages at the same time. Was hitting this _again_ in https://github.com/php/php-src/pull/23105.