Social network field doesn't work correctly if default value is not chosen

Problem/Motivation

When adding a Social media field via Layout Builder, if a default value for the Social network select list is not configured, the Profile link field disappears upon selection of a network. This prevents users from completing the field correctly, creating confusion and broken functionality.

Steps to reproduce

1. Create a field using the Social media field type (e.g., a composite field with Social network and Profile link).
2. Add this field to a block that is placed via Layout Builder.
3. Do not configure a default value for the Social network dropdown.
4. Try to edit the block and choose any option from the Social network field.
5. Observe that the Profile link field disappears or is not shown.