Curl 8.6.0 doesn't allow unsetting of the `-w` field.

### I did this

`curl -w '' http://example.com`
```
curl: option -w: blank argument where content is expected
curl: try 'curl --help' for more information
```

### I expected the following

The website to return with no additional output

### curl/libcurl version

curl 8.6.0

### operating system

Arch Linux 20240101.0.204074 (the latest arch linux)