Check if the file exists before adding it

ZipKit creates a placeholder record when add_file is called, this record is then filled with the content that's passxed to write. But if the blob's file doesn't exist then an error is rased and the placeholder is never filled. This results in a ZIP that has a place in its catalog for the blob, but no contant for it, which makes it invalid.

app/models/account/data_transfer/blob_file_record_set.rb

@@ -9,11 +9,11 @@ class Account::DataTransfer::BlobFileRecordSet < Account::DataTransfer::RecordSe
     end
 
     def export_record(blob)
-      zip.add_file("storage/#{blob.key}", compress: false) do |out|
-        blob.download { |chunk| out.write(chunk) }
+      if blob.service.exist?(blob.key)
+        zip.add_file("storage/#{blob.key}", compress: false) do |out|
+          blob.download { |chunk| out.write(chunk) }
+        end
       end
-    rescue ActiveStorage::FileNotFoundError
-      # Skip blobs where the file is missing from storage
     end
 
     def files