Image extensions property not always working inside set inside collection

[I-Valchev]

For some reason, the extensions setting of an image does not always work when the image is inside a set that is inside a collection.

Example output:

@bolt/_partials/fields/image.html.twig line 23
"collections[content][picture_story][1][image]"
@bolt/_partials/fields/image.html.twig line 109
Bolt\Configuration\Content\ContentType {#265 ▼
  #items: array:5 [▼
    0 => "gif"
    1 => "jpg"
    2 => "jpeg"
    3 => "png"
    4 => "svg"
  ]
}
@bolt/_partials/fields/image.html.twig line 23
"collections[content][picture_story][2][image]"
@bolt/_partials/fields/image.html.twig line 109
[]

The 2nd one should not be empty. It should be the same as the first.