set() and append() generates strange result...

[KarelWintersky]

$data = new \Dflydev\DotAccessData\Data();

$data->set('b.d', [
    'a' =>  5,
    'b' =>  7
]);
$data->append('b.d', [
    'c' =>  2,
    'd' =>  4
]);

var_dump(
    $data->get('b.d')
);

Result is:

array(3) {
  ["a"]=>   int(5)
  ["b"]=>   int(7)
  [0]=>
  array(2) {
    ["c"]=>     int(2)
    ["d"]=>    int(4)
  }
}

although it is logical to expect the result:

array(3) {
  ["a"]=>   int(5)
  ["b"]=>   int(7)
  ["c"]=>   int(2)
  ["d"]=>   int(4)
  } 
}