Handle non-decoded image features
### Link

https://huggingface.co/datasets/society-ethics/LILA

### Description

The dataset viewer expects images to be PIL images, but since the HF Datasets library allows non-decoded images (with `decode=False`) this is not always the case. At the moment, if an image feature is not decoded, the viewer fails with the following error in the UI:

```
Error code:   RowsPostProcessingError
```

In the backend, the error is:
![image](https://user-images.githubusercontent.com/6765188/199774586-c3fcc202-5c93-48d0-b010-29ca7485c6b6.png)

Handle non-decoded image features: ### Link

https://huggingface.co/datasets/society-ethics/LILA

### Description

The dataset viewer expects images to be PIL images, but since the HF Datasets library allows non-decoded images (with `decode=False`) this is not always the case. At the moment, if an image feature is not decoded, the viewer fails with the following error in the UI:

```
Error code:   RowsPostProcessingError
```

In the backend, the error is:
![image](https://user-images.githubusercontent.com/6765188/199774586-c3fcc202-5c93-48d0-b010-29ca7485c6b6.png)
