Parser fails on OutOfOrderTable with leading whitespace #263

 [[a.b.c]]  # note: this line starts with a space character
[a.b]

>>> import tomlkit
>>> tomlkit.parse(" [[a.b.c]]\n[a.b]")

Traceback (most recent call last):
  File "env\Lib\site-packages\tomlkit\parser.py", line 165, in parse
    body.append(key, value)
  File "env\Lib\site-packages\tomlkit\container.py", line 262, in append
    current.append(k, v)
  File "env\Lib\site-packages\tomlkit\items.py", line 1600, in append
    m = re.match("(?s)^([^ ]*)(.*)$", _item.trivia.indent)
                                      ^^^^^^^^^^^^
AttributeError: 'OutOfOrderTableProxy' object has no attribute 'trivia'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "env\Lib\site-packages\tomlkit\api.py", line 83, in parse
    return Parser(string).parse()
           ^^^^^^^^^^^^^^^^^^^^^^
  File "env\Lib\site-packages\tomlkit\parser.py", line 167, in parse
    raise self.parse_error(ParseError, str(e)) from e
tomlkit.exceptions.ParseError: 'OutOfOrderTableProxy' object has no attribute 't
rivia' at line 2 col 5