Description:
------------
Tested on:
PHP 5.6.27-1~dotdeb+7.1 (cli) (built: Oct 15 2016 01:36:00)
PHP 7.0.12-1~dotdeb+8.1 (cli) ( NTS )

mysqli_connect_errno() and $mysql->connect_errno are not set at all after a successful persistent connection is re-connected.

In the example provided, the 3rd call to "new mysqli" is re-using the connection from the first call, however after the 3rd "new mysqli", mysqli_connect_errno() still returns the error code from the 2nd call, rather than returning 0 for a successful reconnection. This makes it virtually impossible to tell if the 3rd connection succeeded or not for proper application level error handling.

Note: This also effects mysqli_connect_error() and $mysqli->connect_error

Test script:
---------------
$server	= 'p:192.168.1.99';
$user	= 'USERNAME';
$pass	= 'PASSWORD';
$db	= 'DATABASE';

$mysql_1 = @new mysqli($server, $user, $pass, $db);
var_dump(mysqli_connect_errno());
@$mysql_1->close();

$mysql_2 = @new mysqli('DOESNT-EXIST', $user, $pass, $db);
var_dump(mysqli_connect_errno());
@$mysql_2->close();

$mysql_3 = @new mysqli($server, $user, $pass, $db);
var_dump(mysqli_connect_errno());
@$mysql_3->close();

Expected result:
----------------
int(0)
int(2005)
int(0)


Actual result:
--------------
int(0)
int(2005)
int(2005)