Description:
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Trying to use functions like is_dir(), is_file(), or any other stat() based function is failing when using an ssh2.sftp resource. Sample warning:

PHP Warning:  filemtime(): stat failed for ssh2.sftp://Resource id #5/etc/issue.net in /home/dougal/test/ssh.php on line 54

Using PHP 7.0.1, php-ssh2 0.12-dev

The same code works fine on a system running PHP 5.6.14 and php-ssh2 0.12


Test 

Test script:
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<?php
$user = "myusername";
$pass = "mypassword";
$host = "localhost";
$path = "/some/file/that/exists";

$session = ssh2_connect($host, 22);
ssh2_auth_password($session, $user, $pass);
$sftp = ssh2_sftp($session);

$sshpath = "ssh2.sftp://$sftp$path";

$stat = stat($path); // works
$statpath = stat($sshpath); // doesn't work
$stat_sftp = ssh2_sftp_stat($sftp, $path); // works

$stream = fopen($sshpath, 'r');
$stat_stream = fstat($stream); // works


Expected result:
----------------
There should be no warnings. stat(), is_file(), is_dir(), etc. should return correct results for $sshpath.


Actual result:
--------------
PHP Warning:  stat(): stat failed for ssh2.sftp://Resource id #5/home/dougal/testfile.txt in /home/dougal/test/ssh-test.php on line 13