Block entity_field renders entity field twice.

Problem/Motivation

Using the block entity_field (Drupal\ctools_block\Plugin\Block\EntityField) causes creation of the render array twice due to the fact that the field->view is executed once in blockAccess() and once in build().

This is introduced in #2804165: Missing check for empty field when building ctools block.

This causes issues when an entity reference field to i.e. a webform is used, where validation and submissions are handled twice because the ->view function gets called twice.

Proposed resolution

Either reuse the created render array in build() again or use access() hook only for access and handle emptyness of fields somewhere else (in build() ?).

Remaining tasks

Implement solution.