Comment generated by email reply will not respect line breaks

The initial comment generated by the email reply did not include any line breaks. Even after trying to edit the comment, add line breaks/paragraphs, and saving -- it will not apply them.

See link below:

https://github.com/fourkitchens/el-ocp-style/commit/0c59d6aceeaa5b5e2e5a3d37cc8a795d9f950a6d#commitcomment-3368080

Start with the linked commit comment to reproduce the missing line breaks in a comment generated from an email reply. Trace how the plain-text email is parsed and define done as preserving paragraph and line-break formatting in the resulting comment, including after editing and saving.

索引モデルが issue の本文から書いたものです。