Avoid errors if field structure is unexepcted

Problem/Motivation

If the field template is not in the expected structure, this or other similar errors can happen:

Error: Attempt to assign property "_attributes" on array in Drupal\paragraphs_collection\Plugin\paragraphs\Behavior\ParagraphsGridLayoutPlugin

Steps to reproduce

For example combine with another plugin that changes the field render array to something else.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes