Image gen issue mitigation — AI Roguelite Steam update #771518

Wombo image gen was down for several hours. The image gen was broken in an unconventional way, where it would allow you to download a PNG file, but the PNG file would be corrupted. This update prevents that kind of issue from breaking game logic, so you can still at least play the game without getting error messages. It also lets the game automatically delete corrupted PNG files so that they may be generated if you reload that save. At almost the exact time I pushed this update, Wombo was fixed again, so there should be no change in behavior for those reading this. Note that if this happens in the future, Stable Horde is a good fallback for free image generation. Their response times seem to have greatly improved from how it was several months ago.