[php-src] Issue #12971: `restore_xxx_handler()` does silently return even if there is no handler to restore

Issue: https://github.com/php/php-src/issues/12971 Author: mvorisek ### Description The following code: repro: https://3v4l.org/DDulh ```php <?php restore_error_handler(); restore_error_handler(); restore_error_handler(); restore_exception_handler(); restore_exception_handler(); restore_exception_handler(); ``` Resulted in this output: ``` ``` But I expected this output instead: ``` php warning for each restore_xxx_handler() call if there is no handler to restore ``` The warnings are important to be inform the developer the operation is probably not wanted (ie. handler was never added). ### PHP Version any ### Operating System any