Miscounting lines with mismatched columns (csv-core)

Example:

https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=b2865b0972382499147f9f8e9eb43e84

Output:

```
line: 2, fields: ABC
line: 3, fields: a1b1c1
line: 4, fields: a2
line: 4, fields: a3b3c3d3
```

Expected (& should it not start from line 1?):

```
line: 2, fields: ABC
line: 3, fields: a1b1c1
line: 4, fields: a2
line: 5, fields: a3b3c3d3
```