OpenPGP_GPG::get_keys() fails if key is not specified

I have a issue when calling gnupg_get_keys without specifying $key_id. Two single quotes get added to the end of the gpg command line where the $key_id would have been if specified. This results in the following gpg error:

gpg: error reading key: Invalid user ID

The issue is in gnupg_exec, in the bit of code that parses the $options array:

  foreach ($options as $k => $vs) {
    foreach (is_array($vs) ? $vs : array($vs) as $v) {
      if ($v !== FALSE) {
        $command .= !is_numeric($k) ?
          ' --'. $k . ($v === TRUE ? '' : ' ' . escapeshellarg((string)$v)) :
          ' ' . escapeshellarg((string)$v);
      }
    }
  }

The escapeshellarg function is returning a string of two single quotes (''), not an empty string. The two single quotes get added to the end of the gpg command line.

Replacing the above bit of code with the following bit fixes this issue for me:

  foreach ($options as $k => $vs) {
    foreach (is_array($vs) ? $vs : array($vs) as $v) {
      if ($v !== FALSE) {
        $command .= !is_numeric($k) ?
          ' --'. $k . ($v === TRUE ? '' : ' ' . escapeshellarg((string)$v)) :
          ' ' . (!empty($v) ? escapeshellarg((string)$v) : '');
      }
    }
  }

However, if there are any instances where the $options key is numeric and the value is an empty string and the command line really should have two single quotes appended, this change could break that. I haven't tested all the other functions that call gnupg_exec. FYI, I'm using PHP 5.2.6. This sounds like it may be related to the issue pokey was experiencing: http://drupal.org/node/366982.