Fix issue where `--download-game` throws an error when downloading free games

[triple-j]

Downloading of free games stopped working.

Running itch-download --download-game "https://nomnomnami.itch.io/charm-studies" --api-key xxx returns the following error:

Traceback (most recent call last):
  File "/root/.cache/pypoetry/virtualenvs/itchiodl-9TtSrW0h-py3.8/bin/itch-download", line 6, in <module>
    sys.exit(main())
  File "/app/itchiodl/downloader/__main__.py", line 67, in main
    lib.load_game(matches.group(1), matches.group(2))
  File "/app/itchiodl/library.py", line 56, in load_game
    self.games.append(Game(k))
  File "/app/itchiodl/game.py", line 22, in __init__
    self.data = data["game"]
KeyError: 'game'

In commit c652516eec390606d81350dd6f6a1c32e52cf747 a check was added to determine if a game was not purchased. This was accomplished via the uploads/ endpoint. Unfortunately that endpoint replaced the call to the game data endpoint that we need to download the game. This adds the game data endpoint call back in.