Description:
------------
Trying to insert a date into a table using TO_DATE function returns an error if attribute PDO::ATTR_ORACLE_NULLS is set to PDO::NULL_TO_STRING and no rows are inserted. 
If this attribute is not set, no error is returned and no rows are inserted also.

Reproduce code:
---------------
/*
create table test_pdo
(
name char(10) not null,
some_d date not null
)
*/

$ifx = new PDO('informix:host=db.kisise;service=1526;database=krediit;server=db_krediit;protocol=onsoctcp; EnableScrollableCursors=0','someuser','somepass');
$ifx->setAttribute(PDO::ATTR_ORACLE_NULLS, PDO::NULL_TO_STRING);

$istmt = $ifx->prepare('insert into test_pdo (name, some_d) values(:n, TO_DATE(:d,"%d.%m.%Y"))');
$istmt->execute(array('n' => 'test', 'd' => '02.02.2002'));


Expected result:
----------------
The row is inserted into a table

Actual result:
--------------
Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[]: <<Unknown error>>: 0  (SQLExecute[0] at /root/php/PDO_INFORMIX-1.1.0/informix_statement.c:720)