Issue: Media used as fieldGroup inside a fieldGroup not working

[BetterStoryTimer]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:
Creating a fieldGroup with a nested fieldGroup of type media/image:

{
      "id": "selectedWorks",
      "labelField": "workTitle",
      "fields": [
        {
          "title": "Work Title",
          "name": "workTitle",
          "type": "string",
          "single": true
        },
        {
          "title": "Selected Media",
          "name": "selectedMedia",
          "type": "block",
          "fieldGroup": [
            "mediaSource"
          ]
        }
      ]
    },
    {
      "id": "mediaSource",
      "labelField": "sourceName",
      "fields": [
        {
          "title": "Source Name",
          "name": "sourceName",
          "type": "string",
          "single": false
        },
        {
          "title": "Source Path",
          "name": "sourcePath",
          "type": "image",
          "isPreviewImage": false,
          "multiple": false
        }
      ]
    }

Than assign it to my contentType:

 {
      "name": "dummypage",
      "pageBundle": true,
      "previewPath": null,
      "fields": [
        {
          "title": "Title",
          "name": "title",
          "type": "string"
        },
        {
          "title": "Works Media Selection",
          "name": "worksMediaSelection",
          "type": "block",
          "fieldGroup": [
            "selectedWorks"
          ]
        },
        {
          "title": "type",
          "name": "type",
          "type": "string"
        } 
      ]
    },

Expected behavior
Creating a list of images inside my selected Works Album and list all the picture below.

Screenshots
Resulting in just returning the Source Name.

---
title: dummy new one
worksMediaSelection:
  - workTitle: work
    selectedMedia:
      - sourceName: source
        fieldGroup: mediaSource
    fieldGroup: selectedWorks
type: dummypage
---

Desktop (please complete the following information):

• OS: OSX 13.2
• Browser Chrome, Safar...
• Version [e.g. 22]

Additional context
Add any other context about the problem here.

[estruyf]

@anthonykasabian, thanks for opening this issue; it was indeed a bug in the image field and mapping to the sub-block of its contents.

I have investigated it and came up with a fix. Feel free to give it a try in the latest beta version.