Net::HTTP always returns ASCII-8BIT encoding. File.read auto-detects the encoding. This leads to an encoding inconsistency between a fresh download, and a cached download. This commit ensures all downloaded files are treated equally, by always returning the cached version from the filesystem, even during initial download.
One symptom of this problem is during theme exports: https://meta.discourse.org/t/116907
Related ruby ticket: https://bugs.ruby-lang.org/issues/2567