Description:
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Using PDO::FETCH_KEY_PAIR as an argument to PDOStatement->setFetchMode() cause an error.

Note : PDO::FETCH_KEY_PAIR works well when used directly as an argument to fetchAll() without setFetchMode().

Reproduce code:
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$dbh = new PDO($dsn, $login, $password);
$sql = 'SELECT id, login FROM user u';
$results = $dbh->query($sql);
$results->setFetchMode(PDO::FETCH_KEY_PAIR);
print_r($results->fetchAll());

Expected result:
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An associative array ('id' => 'login')

Actual result:
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SQLSTATE[22003]: Numeric value out of range: Invalid fetch mode specified