CLI cannot process multiple passed files with the same name

#### Version information:
```
go-ipfs version: 0.9.0
Repo version: 11
System version: amd64/linux
Golang version: go1.16
```

#### Description:

For https://github.com/bmwiedemann/ipfs-iso-jigsaw/blob/prehashnodirs/prehash.py#L53 I am trying to add files without directories into ipfs and noticed that directories are not printed in output, but what is worse, files are silently not added (or at least not reported)

```
mkdir -p /tmp/x/{1,2}
echo x > /tmp/x/1/x
echo y > /tmp/x/2/x
ipfs add -n --raw-leaves -- /tmp/x/1/x /tmp/x/2/x
added bafkreib3wkv3nhv3e7574y6hmolcjrxmlyzrxba2lpemh26bbojil2iio4 x
```