Description:
------------
gnupg_keylistiterator segfaults on iteration.

Test script:
---------------
<?php
// create a new iterator for listing all public keys that matches 'example'
$iterator = new gnupg_keylistiterator("example");
echo "test";
foreach($iterator as $fingerprint => $userid){
    echo $fingerprint." -> ".$userid."\n";
}
?>

Expected result:
----------------
fingerprint -> userid

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