Binary download fails if previous download attempt fails

[danieltharp]

Maybe a little quality of life enhancement to consider.

I was going through initial setup on a new Mac and ran a test makelove build and because I'd forgotten to install the certifi package from pip, the download failed. However, makelove had made the folder in /Users/{user}/Library/Caches/makelove/love-binaries/{version}/macos. When I fixed the issue and reran, it assumed the file was in there even though the directory was empty. It may be worth checking for the actual binary rather than the simple existence of the folder. I can probably submit a PR for this if it would help.