Description:
------------
If the mysql bind result mechanism is used to retrieve results from a column that is declared with sub-second precision, the extra precision is lost. This only happens with mysqlnd, not libmysqlclient, and it doesn't happen if fetch_assoc() is called.

Test script:
---------------
CREATE TABLE test (
  datetime_col datetime(3) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

commit;

insert into test values ('2017-12-05 01:02:03.456');
insert into test values ('2017-12-05 07:08:09.000');

commit;

<?php
$conn = new mysqli($servername, $username, $password, $dbname, $port);
$sql = "SELECT datetime_col from test";
$stmt = $conn->prepare($sql);
$stmt->bind_result($result);
$stmt->execute();

while($stmt->fetch()) {
        var_dump($result);
}
?>


Expected result:
----------------
string(23) "2017-12-05 01:02:03.456"
string(23) "2017-12-05 07:08:09.000"

Actual result:
--------------
string(19) "2017-12-05 01:02:03"
string(19) "2017-12-05 07:08:09"