Fix source file uploading in v1.7.0

[artem-vavilov]

After updating from v1.6.0 to v1.7.0, JSON files began to upload corrupted.

Issues

1. #add_file New JSON files are corrupted as their JSON data content has been replaced with the local file path string.

Original file content	Uploaded file content
{"data": "Data"}	"/path/to/file.json"

2. #update_or_restore_file Returns error:

{
  "errors" => [
    "error" => {
      "key"    => "storageId",
      "errors" => [
        "code"    => "fileInvalid",
        "message" => "Uploaded file \"file.json\" is invalid and cannot be processed"
      ]
    }
  ]
}