Three regressions when editing a page containing a list (Grav 1.7.6 compared to 1.6.31)

Hello,

We noticed 3 minor regressions in Grav 1.7.6 compared to Grav 1.6.31 when editing a page containing a list :

1. When a list is collapsed, the last item of the list overflows his container.
2. When a collapsed item is revealed, the text in the editor is invisible until we click inside the editor.
3. When adding a new item in the list, uploading an image cause an error _Undefined index: *_.

Here is a simple blueprint _mytest.yaml_ used for testing :
```
extends@: default

form:
fields:
tabs:
type: tabs
active: 1

fields:
content:
type: tab
title: My Blueprints
fields:
header.title:
unset@: true
content:
unset@: true
header.media_order:
unset@: true
header.sections:
label: Sections
type: list
collapsed: true
style: vertical
fields:
.image:
type: file
label: Image
destination: 'self@'
.text:
type: markdown
label: Text
```

Here is a _mytest.md_ page. You can use any image.
```
---
title: mypage
sections:
-
text: 'My text'
image:
140x100.png:
name: 140x100.png
type: image/png
size: 333
path: 140x100.png
---
```

1. Overflow

2. Invisible text after revealing an item

The text appears after a click inside the editor

3. After adding a new item, this error appears when uploading a new image. It's possible to bypass by (1) adding a new empty item, (2) saving the page and (3) uploading the image.

Thank you for your time! :)