Description:
------------
openssl_pkcs12_export_to_file crash with "Segmentation fault: 11"


Code works without segfault if:

* remove the line "$privateKey = new PrivateKey($privateKey);"
* var_dump something after openssl_pkcs12_export_to_file


Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x000000012b86af59
0x00000001001f0c25 in gc_zval_possible_root ()
(gdb) bt
#0  0x00000001001f0c25 in gc_zval_possible_root ()
#1  0x00000001001e2046 in zend_hash_bucket_delete ()
#2  0x00000001001e20ac in zend_hash_graceful_reverse_destroy ()
#3  0x00000001001c8027 in shutdown_executor ()
#4  0x00000001001d6227 in zend_deactivate ()
#5  0x000000010017d045 in php_request_shutdown ()
#6  0x000000010025f7d7 in do_cli ()
#7  0x000000010025e354 in main ()

Test script:
---------------
<?php

class PrivateKey {

    public $data;

    public function __construct($data) {
        $this->data = $data;
    }

    public function __toString() {
        openssl_pkey_export($this->data, $output);
        return $output;
    }

}

$csr = openssl_csr_new([], $privateKey);
$certificate = openssl_csr_sign($csr, NULL, $privateKey, 1);

$privateKey = new PrivateKey($privateKey);
openssl_pkcs12_export_to_file($certificate, '/tmp/test.p12', $privateKey, '');

# var_dump('bar');

Expected result:
----------------
Nothing

Actual result:
--------------
Segmentation fault: 11