Attachments from fd_embedded_json are not correctly parsed

[onestep]

Prerequisites:

• Account with _GM_setData preload.

Steps to reproduce:

1. open Inbox folder
2. receive email with attachment from some another account
3. reload page
4. navigate to new received email

Actual result: Attachments data are processed incorrectly: attachment_id is "a", other properties are undefined.

[onestep]

I've opened a pull request #674 with a fix. I decided to keep parse_fd_attachments as is, but it can be renamed to parse_fd_request_payload_attachments if needed.

[josteink]

Fixed in #673 and published on npmjs as v1.0.18.