Extract zip: Ignore content type and check extension

It appears that zip archives from Windows sometimes come with content type application/x-zip-compressed. In that case, the user cannot unzip the archive because we check for application/zip only:

{"error":"Incompatible content type for extracting: application/x-zip-compressed","localizedError":"Incompatible content type for extracting: application/x-zip-compressed"}

This MR changes the first test to inspect only that file.extension == '.zip' (before loading bytes) and then wraps the unzipping operation in a try () { } block.