`image` column not automatically inferred if image dataset only contains 1 image

[apolinario]

Describe the bug

By default, the standard Image Dataset maps out file_name to image when loading an Image Dataset.

However, if the dataset contains only 1 image, this does not take place

Steps to reproduce the bug

Input
(dataset with one image multimodalart/repro_1_image)

from datasets import load_dataset
dataset = load_dataset("multimodalart/repro_1_image")
dataset

Output:

DatasetDict({
    train: Dataset({
        features: ['file_name', 'prompt'],
        num_rows: 1
    })
})

Input
(dataset with 2+ images multimodalart/repro_2_image)

from datasets import load_dataset
dataset = load_dataset("multimodalart/repro_2_image")
dataset

Output:

DatasetDict({
    train: Dataset({
        features: ['image', 'prompt'],
        num_rows: 2
    })
})

Expected behavior

Expected to map file_name → image for all dataset sizes, including 1.

Environment info

Both latest main and 2.16.0