Fix numeric arrays load

All arrays should be loaded as objects to read paths with numeric array indexes later.
This patch is a replace for https://github.com/joomla-framework/registry/pull/10

  public function testGetWithNumericKey()
  {
      $a = new Registry;
      $b = new \stdClass();
      $b->array1 = array("x","y","z");
      $a->loadObject($b);
      $this->assertEquals('x', $a->get('array1.0'), 'Line: ' . __LINE__ . ' get method should work.');
  }