Description:
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using is_dir with ssh2.sftp:// will end with the error below.
operations like opendir work fine

Test script:
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$conn = ssh2_connect($ssh_host);
$status = ssh2_auth_pubkey_file($conn, $ssh_user, $ssh_pubkey_file, $ssh_privkey_file);
$sftp = ssh2_sftp($conn);

is_dir("ssh2.sftp://".intval($sftp)."/path/to/file");

Expected result:
----------------
it should not segfault the script

Actual result:
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/usr/local/httpd-2.4-php-7.3/bin/httpd: symbol lookup error: /usr/local/php-7.3-httpd-2.4/lib/php/20180731-zts-debug/ssh2.so: undefined symbol: php_ssh2_sftp_attr2ssb