Description:
------------
When using ::bindParam() or ::bindValue(), as soon as a null or PDO::PARAM_NULL is used, the driver retains the is_null value for the rest of the calls.



Reproduce code:
---------------
Source code sample:
http://zirzow.dyndns.org/patches/mysql_statement.c.phps

Patch:
http://zirzow.dyndns.org/patches/mysql_statement.c.patch

Expected result:
----------------
array(3) {
  [0]=>
  array(1) {
    ["bar"]=>
    string(3) "foo"
  }
  [1]=>
  array(1) {
    ["bar"]=>
    NULL
  }
  [2]=>
  array(1) {
    ["bar"]=>
    string(3) "qaz"
  }
}


Actual result:
--------------
array(3) {
  [0]=>
  array(1) {
    ["bar"]=>
    string(3) "foo"
  }
  [1]=>
  array(1) {
    ["bar"]=>
    NULL
  }
  [2]=>
  array(1) {
    ["bar"]=>
    NULL
  }
}