Check the EIA response before saving it as a workbook

[arpitjain099]

eia_7a_download writes requests.get(url).content straight to coalpublic<year>.xls without looking at the status. When EIA answers 404, the error page gets saved as the workbook, and read_eia7a later raises the "see issues/230" ValueError. So a plain missing-file response is reported to the user as the XML-format problem from that issue, which is a different thing entirely.

The folder was also created before the request, so after a failed download the caller's if not os.path.exists(expected_7a_folder) guard stops trying and find_file_in_folder fails on an empty directory instead.

Now it calls raise_for_status() first, only creates the folder and writes once the response is good, and the log line names the actual error.

I checked both paths with requests.get patched: a 404 used to leave a 75-byte coalpublic2016.xls starting <html><head><title>4, and now leaves nothing and logs "404 Not Found for url: ...". A 200 still writes the file as before.

The except is now except Exception as e rather than bare, and the message is a warning rather than info, since a failed download does change what the rest of the run can do. Happy to drop that part if you would rather keep it quiet.