Issue with parsing when two consecutive replies are on email from same person

When a person replies twice on the same thread via email consecutively, second time the email parsing seems buggy.

For example, see [this](https://github.com/duckduckgo/zeroclickinfo-goodies/issues/2834#issuecomment-205969733).

檢視 zeroclickinfo-goodies issue #2834 中連結的範例，並重現同一個人連續傳送兩則回覆時對 thread 的解析。追蹤 parser 對第二則回覆的處理，並為該情況新增覆蓋；當兩則回覆都能在沒有報告的損壞情況下完成解析時，即表示完成。

由索引模型根據 Issue 內容生成。