Handling error responses vs empty report responses

[agaman]

It turns out that an empty response URL with a successful response is actually just an empty report.

https://docs.microsoft.com/en-us/bingads/reporting-service/reportrequeststatus

This changeset handles 3 cases for the incremental downloading of a report:

• A successful request with a download_url: download, advance the sync date, clear the request_id
• A successful request without a downlod_url: advance the sync date, clear the request_id
• An unsuccessful request: clear the request_id

[nick-mccoy]

👍