fix: fix bug in human readable errors

[Mishura4]

The error parser would stop at the first field (here "thumbnail") on something like this, and show "Invalid Form Body":

{
    "message": "Invalid Form Body",
    "code": 50035,
    "errors": {
        "embeds": {
            "0": {
                "thumbnail": {
                    "url": {
                        "_errors": [
                            {"code": "URL_TYPE_INVALID_URL", "message": "Not a well formed URL."}
                        ]
                    }
                }
            }
        }
    }
}

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