Description:
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Partially finished unbuffered query for mysql doesn't return any errors.
The problem persists for all current versions of mysqlnd but everything find with 
old libmysqlclient code for all mysql extensions: mysql, mysqli, pdo-mysql.

If I have 100k rows in query and connection dropped at 50k point, there is no 
simple way to see this error in application and handle the problem.

Test script:
---------------
1) create a big table to have several seconds for select * from table execution time
2) run php script
3) kill connection from php to mysql or kill mysqld

<?php
error_reporting(E_ALL);
$link = mysql_connect('localhost', 'root', '');
mysql_select_db('test') or die('Could not select database');

// Performing SQL query
$query = 'SELECT * FROM x;';
$result = mysql_unbuffered_query($query) or die('Query failed: ' . mysql_error());

while ($line = mysql_fetch_array($result, MYSQL_ASSOC)) {
}

echo mysql_error($link) . PHP_EOL;

Expected result:
----------------
Warning about connection problems and
mysql_error should return Query failed: MySQL server has gone away

Everything works correctly for old (non-mysqlnd) extension.

Actual result:
--------------
getting warning:
Warning: Empty row packet body in /root/php5-trunk/test.php on line 10

But empty result for mysql_error($link)