Description:
------------
Hey,

Only the first multiple-result-set query on a given pdo connection works as expected; subsequent queries always claim to have only one result-set (although they have many). This does not happen if PDOStatement used to issue the query is unset(). The communication with the database is correct (checked with wireshark); this is an api issue.

Test script:
---------------
$sql = 'SELECT 123; SELECT 42; SELECT 999';
$pdo = new PDO('mysql:dbname=xxx;host=xxx', 'xxx', 'xxx');

$stmt = $pdo->query($sql);
var_dump($stmt->nextRowset()); /* returns true, as expected */
var_dump($stmt->nextRowset()); /* returns true, as expected */
var_dump($stmt->nextRowset()); /* returns false, as expected */
$stmt->closeCursor();
/* unset($stmt); uncomment this line to make stuff "work" */

$stmt = $pdo->query($sql);
var_dump($stmt->nextRowset()); /* expected: true; got: false */
var_dump($stmt->nextRowset()); /* expected: true; got: false */
var_dump($stmt->nextRowset());
$stmt->closeCursor();
/* unset($stmt); uncomment this line to make stuff "work" */

Expected result:
----------------
bool(true)
bool(true)
bool(false)
bool(true)
bool(true)
bool(false)

Actual result:
--------------
bool(true)
bool(true)
bool(false)
bool(false)
bool(false)
bool(false)