Description:
------------
If the compressed packet payload is bigger than 0xffffff (because DEFLATE increased the size), then the payload length will overflow on 24 bit boundary and PHP ends up with a warning and fails.

Test script:
---------------
ini_set("memory_limit", "1G");
$db = mysqli_init();
$db->real_connect(HOST, USER, PASS, DB, 3306, null, MYSQL_CLIENT_COMPRESS);
$q = $db->prepare("INSERT INTO tmp (text) VALUES (?)");
$n = null;
$q->bind_param('b', $n);
$x = file_get_contents("/dev/urandom", 0, null, -1, 0xffffff - 1);
$q->send_long_data(0, $x);
$q->execute();

Expected result:
----------------
Successful insert in database...

Actual result:
--------------
Warning: Error while sending STMT_SEND_LONG_DATA packet. PID=%d in %s on line %d

(Doesn't matter if QUERY, PREPARE or STMT_SEND_LONG_DATA packet or what ever; issue is always the same.)