Duplicate comments in database file

To reproduce:

1. Open a file and add a comment (for i.e. `first` at offset 0).
2. Save and quit with `:x`.

The `.dz6` file generated is as follows:
```toml
bookmarks = []

[[comment_name_list]]
offset = 0
comment = "first"

[comments]
0 = "first"
```
As shown above, currently both `comment_name_list` and `comments` store the same comment.