Doesn't play nice with CarrierWave's #move_to_cache

CarrierWave has an option for moving files to its cache rather than copying them:

https://github.com/carrierwaveuploader/carrierwave#large-files

When using `move_to_cache`, if you're using `File.open` to open the file uploaded for the original resource, CarrierWave will move that file to its cache (and later delete it), thus destroying the original resource's file.