Fix bug: tmp_name check

[mpyw]

The form names containing tmp_name may cause errors on fopen() call.

<form method="post" action="" enctype="multipart/form-data">
    <input type="submit">
    <input type="file" name="file[x][tmp_name][y]">
</form>

So we should check if tmp_name is not array using !is_array().

[fabpot]

Closing as Goutte 4 has just been released and it does not depend on Guzzle anymore.