Description:
------------
This warning makes sense for the other block cipher modes, but when using MCRYPT_MODE_ECB the initialization vector is not used at all, so it is misleading to recommend using one.  In fact there should be a notice/warning when an IV is supplied with mode MCRYPT_MODE_ECB to alert that the IV is ignored.

Reproduce code:
---------------
<?php
$input = 'to be encrypted';
$mkey = hash('sha256', 'secret key', TRUE);
$data = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $mkey, $input, MCRYPT_MODE_ECB);
?>

Expected result:
----------------
no warning

Actual result:
--------------
PHP Warning:  mcrypt_encrypt(): Attempt to use an empty IV, which is NOT recommend