fix(ObjectControl): hotfix nested object validation

[demshy]

Summary

This a quick patch for #7383 that happened after the validation rework in #7374

I have tested against most of the cases that I could think of and it seems to be ok.

Test plan

This is the config that I tested with, changing required on/off and trying multiple nested depths

{name: pageHero, label: Page hero, widget: object, collapsed: true, summary: '{{fields.title}}', fields: [
      {name: title, widget: string, i18n: true, required: false, hint: 'if empty, page title will be used'},
      {name: description, widget: string, i18n: true, required: false, hint: 'if empty, page description will be used'},
      {name: button, widget: object, i18n: true, fields: [
        {name: text, widget: string, i18n: true, required: false},
        {name: href, widget: string, i18n: true, required: false},
      ]},
    ]}

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[demshy]

This should be followed by a PR with e2e tests for this feature.