Avoid rare NoneType is not subscriptable error

[frozenpandaman]

Apparently this is possible, reported by a user:

Traceback (most recent call last):
  File "C:\Users\Kyle\s3s\s3s.py", line 2060, in <module>
    main()
  File "C:\Users\Kyle\s3s\s3s.py", line 2028, in main
    check_if_missing(which, blackout, test_run, skipprefetch) # monitoring mode hasn't begun yet
  File "C:\Users\Kyle\s3s\s3s.py", line 1484, in check_if_missing
    fetch_and_upload_single_result(id, noun, isblackout, istestrun)
  File "C:\Users\Kyle\s3s\s3s.py", line 1401, in fetch_and_upload_single_result
    post_result(result, False, isblackout, istestrun) # not monitoring mode
  File "C:\Users\Kyle\s3s\s3s.py", line 1193, in post_result
    payload = prepare_battle_result(results[i]["data"], ismonitoring, isblackout, overview_data)
  File "C:\Users\Kyle\s3s\s3s.py", line 500, in prepare_battle_result
    full_id = utils.b64d(battle["id"])
TypeError: 'NoneType' object is not subscriptable

Which would mean battle had a vsHistoryDetail key in it, but then that in turn was null?

s3s/s3s.py

Lines 496 to 500 in fdd5ae8

	battle = battle["vsHistoryDetail"]
	## UUID ##
	##########
	full_id = utils.b64d(battle["id"])

Sounds like an error on Nintendo's end...? Anyway, we should exit gracefully here instead of crashing. To-do.