UsesHashedFileNameWithAutoExtAndProcessor does not retrieve the correct file extension.

[freezy7]

Hello, I found when use autoExtAfterHashedFileName = true, the original method var ext: String? of finding the last "." to determine the extension is not effective because the field after the "@" symbol may contain a "com.onevcat.Kingfisher.xxx" and even include decimal points.

hope this PR is helpful.