Return file handles if it's a file

This should work:

```python
import replicate
from urllib.request import urlretrieve
model = replicate.models.get("stability-ai/stable-diffusion")
version = model.versions.get("27b93a2413e7f36cd83da926f3656280b2931564ff050bf9575f1fdf9bcd7478")
out = version.predict(prompt="wavy colorful abstract patterns, cgsociety"
background = Image.open(out)
```

See #48 #66