FIX: destroy optimized images that cant' be migrated to new scheme

Since we can always recompute an optimized image from the original upload, there's no need to keep optimized images that are generating errors.

app/models/optimized_image.rb

@@ -220,6 +220,8 @@ class OptimizedImage < ActiveRecord::Base
           end
         rescue => e
           problems << { optimized_image: optimized_image, ex: e }
+          # just ditch the optimized image if there was any errors
+          optimized_image.destroy
         ensure
           file.try(:unlink) rescue nil
           file.try(:close) rescue nil