unicode characters at end of line defect in vimcat

Here is some minimal example
```bash
> echo -e 'ää\n€€\n°°' | vimcat
ä�[0m
€�[0m
°�[0m
```
I remember already having observed this bug some years ago and it still happens with current vimpager and Vim 9.0.
The same happens with vimpager when it uses passthrough mode.