Input to `BREAKING CHANGE commit requires a body` isn't used

- The input given to `? A BREAKING CHANGE commit requires a body. Please enter a longer description of the commit itself:` isn't used
- This prompt pops up when `Provide a longer description of the change` is skipped
- Potentially related to #718

## Actual Behaviour

- Given the following:

```
$ git cz --allow-empty
cz-cli@4.1.2, cz-conventional-changelog@3.2.0

? Select the type of change that you're committing: feat: A new feature
? What is the scope of this change (e.g. component or file name): (press enter to skip) foo
? Write a short, imperative tense description of the change (max 89 chars):
(25) my very short description
? Provide a longer description of the change: (press enter to skip)

? Are there any breaking changes? Yes
? A BREAKING CHANGE commit requires a body. Please enter a longer description of the commit itself:
My longer description for a breaking change
? Describe the breaking changes:
The breaking change itself
? Does this change affect any open issues? No
[master 58da0e1] feat(foo): my very short description
```

- Running `git log` gives:

```
commit 58da0e199964ec5c50b3521f385deee2d1dfe218
Author: Nicholas Nadeau
Date: Mon Sep 14 21:42:01 2020 -0400

feat(foo): my very short description

BREAKING CHANGE: The breaking change itself
```

- Notice that the `My longer description for a breaking change` provided to the prompt is not part of the git log

## Expected Behaviour

- Alternatively, we can remember to provide a longer description from the start:

```
$ git cz --allow-empty
cz-cli@4.1.2, cz-conventional-changelog@3.2.0

? Select the type of change that you're committing: feat: A new feature
? What is the scope of this change (e.g. component or file name): (press enter to skip) bar
? Write a short, imperative tense description of the change (max 89 chars):
(25) another short description
? Provide a longer description of the change: (press enter to skip)
Now I directly provide a longer description
? Are there any breaking changes? Yes
? Describe the breaking changes:
Here I describe why I broke things
? Does this change affect any open issues? No
[master fcd9863] feat(bar): another short description
```

- `git log` now shows:

```
commit fcd986317222ee08076b10650bcbd5ba16cb377f (HEAD -> master)
Author: Nicholas Nadeau
Date: Mon Sep 14 21:44:04 2020 -0400

feat(bar): another short description

Now I directly provide a longer description

BREAKING CHANGE: Here I describe why I broke things
```

示されているプロンプトのシーケンスを使用して `git cz --allow-empty` で問題を再現し、その後、コマンドラインプロンプトの処理とコミットメッセージの組み立てを調査します。`A BREAKING CHANGE commit requires a body` で入力したテキストが breaking-change の説明とともに `git log` に表示され、最初の body をスキップするケースをテストでカバーできれば、修正は完了です。

索引モデルが issue の本文から書いたものです。