Description:
------------
When issuing a LOAD DATA LOCAL INFILE statement, if the file is missing, mysqli_error() returns the empty string. The same query issued from the command line client returns the following message:

ERROR:
File '/path/to/nonexistent/file.txt' not found (Errcode: 2)

mysqli_errno returns 2000 (CR_UNKNOWN_ERROR)

Reproduce code:
---------------
<?php  
$mysqli = mysqli_init();
$mysqli->options(MYSQLI_OPT_LOCAL_INFILE, 1);
$connect = $mysqli->real_connect('xxx.xxx.xxx.xxx', 'xxxxxxxx', 'xxxxxxxxx', 'mydb');
$query = "
LOAD DATA LOCAL INFILE '/path/to/nonexistent/file.txt' 
INTO TABLE mytable
FIELDS TERMINATED BY ','
OPTIONALLY ENCLOSED BY '\"'
LINES TERMINATED BY '\r\n'
";
$result = $mysqli->query($query);
var_dump($result, $mysqli->errno, $mysqli->error);

// $result: false
// $mysqli->errno: 2000 (unknown error)
// $mysqli->error: "" (empty string)
?>

Expected result:
----------------
I expect to see an error message similar to the one returned by the command-line client, or at least a message that gives a clearer idea of what might have gone wrong.

Actual result:
--------------
Error message is the empty string