Description:
------------
Some simpler devices (e.g. older Cisco Devices, Dell SonicWall firewalls, Motorola RFS 7000 switches) implement the SSH service without any authentication (they show a prompt after the connection is established). If a ssh2_auth_password or ssh2_auth_agent is called on a connection to one of these devices a segfault occurs because libssh2_userauth_list returns NULL.

The problem can be prevented by calling ssh2_auth_none and checking if the return value is TRUE, but I believe the ssh2_auth_password should fail gracefully.

Test script:
---------------
$host = '95.215.46.98';
$port = 2200;
$conn = ssh2_connect($host, $port);
if (!$conn) {
        echo "Error connecting to '{$host}:{$port}'\n";
        die(1);
}
echo "Connected to '{$host}:{$port}'. Trying password authentication\n";
ssh2_auth_password($conn, 'test', 'test');
echo "OK\n";


Expected result:
----------------
Connected to '95.215.46.98:2200'. Trying password authentication
Segmentation fault (core dumped)