Fix compiler error: assignment of member ‘_zend_object_handlers::clone_obj’ in read-only object

struct \_zend_object_value defined in Zend/zend_types.h:
```c
typedef struct _zend_object_value {
	zend_object_handle handle;
	const zend_object_handlers *handlers;
} zend_object_value;
```
In the struct `zend_object_value` `zend_object_handlers declared` as `const`, therefore, we need to enter the auxiliary variable `zend_object_handlers *handlers`