`crane export` creates tar even on failure

### Describe the bug

A tar file is created even though the image failed to be pulled.

### To Reproduce

```sh
# fails
crane export does-not-exist x.tar

# succeeds
file x.tar
```

### Expected behavior

When `crane export some-image some.tar` fails, then it should not create a `some.tar`.

### Additional context

Add any other context about the problem here.

```
❯ crane version
0.20.3
```
