Fixes #5716 az_text_media_paragraph_behavior does not check field group existence

[tadean]

Description

The az_text_media_paragraph_behavior plugin does not check if specific field groups exist before using them. This can cause PHP errors on sites that have diverged from Quickstart's configuration.

This PR checks if the field group structures exist before using them. The null-safe operator cannot be used here since the variables are used in a write context.

Related issues

#5716

How to test

• Create page using text on media paragraphs
• Verify content displays correctly
• Visit /admin/structure/paragraphs_type/az_text_media/display
• Delete one or more of the field groups group_az_column, group_az_title, or group_az_content
• View the page content you created again
• It may display unusually due to the missing field groups, but should not cause a whitescreen error

Types of changes

Arizona Quickstart (install profile, custom modules, custom theme)

• Patch release changes
  • Bug fix
  • Accessibility, performance, or security improvement
  • Critical institutional link or brand change
  • Adding experimental module
  • Update experimental module
• Minor release changes
  • New feature
  • Breaking or visual change to existing behavior
  • Upgrade experimental module to stable
  • Enable existing module by default or database update
  • Non-critical brand change
  • New internal API or API improvement with backwards compatibility
  • Risky or disruptive cleanup to comply with coding standards
  • High-risk or disruptive change (requires upgrade path, risks regression, etc.)
• Other or unknown
  • Other or unknown

Drupal core

• Patch release changes
  • Security update
  • Patch level release (non-security bug-fix release)
  • Patch removal that's no longer necessary
• Minor release changes
  • Major or minor level update
• Other or unknown
  • Other or unknown

Drupal contrib projects

• Patch release changes
  • Security update
  • Patch or minor level update
  • Add new module
  • Patch removal that's no longer necessary
• Minor release changes
  • Major level update
• Other or unknown
  • Other or unknown

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My change requires release notes.

[djcelaya]

I reproduced the error locally using the testing instructions on a vanilla build. I then repeated the steps on another build of this PR and no longer observed the WSOD.