Catch network errors during download-dat

[TylerVigario]

Got an error during updating my Redump DATs today.

Processing "Sony - PlayStation 2"
⠠
thread 'main' panicked at 'Failed to download ZIP: connection closed', src/download_dats.rs:270:10

[alucryd]

I was being lazy here because surf's error does not have the StdError trait, which makes it a pain to handle :P I'll see what I can do.

Edit: There's even an issue about it upstream https://github.com/http-rs/surf/issues/347

[alucryd]

Done, it will simply progress to the next DAT now :)