Description:
------------
Memory seems to be leaking, when extracting public keys from x509 certificates with openssl_pkey_get_public(). Resources do not free automatically, with openssl_pkey_free(), unset(), or null-assignment. 

The leakage is observed on 
PHP 7.1.23 macOS Darwin Kernel Version 18.7.0 + LibreSSL 2.2.7/2.6.5, 
PHP 7.2.24-0ubuntu0.18.04.6 + OpenSSL/1.1.1
PHP 8.0.0-dev Ubuntu + OpenSSL/1.1.1

The test script is provided.

Test script:
---------------
https://gist.github.com/nikita-kun/88b80583a4d12230910040cf2cd3031d

Expected result:
----------------
Constant memory usage

Actual result:
--------------
Memory usage, real: 2097152
Memory usage, real: 4194304
Memory usage, real: 6295552
...
Memory usage, real: 106958848
Memory usage, real: 109056000

Warning: openssl_x509_read(): Supplied parameter cannot be coerced into an X509 certificate! in ./php-src/memleak.php on line 38

Fatal error: Uncaught TypeError: openssl_pkey_free(): Argument #1 ($key) must be of type resource, bool given in ./php-src/memleak.php:41
Stack trace:
#0 ./php-src/memleak.php(41): openssl_pkey_free(false)
#1 ./php-src/memleak.php(56): fastLeakage()
#2 {main}
  thrown in ./php-src/memleak.php on line 41
Killed

OR

"Fatal error: Allowed memory ... exhausted".