Cater for fields with no value

[bobbingwide]

Some of the field types have render methods that access array elements within the field.
They assume that a value has been entered.
When it hasn't then a Fatal error may occur
eg

Fatal error: Uncaught TypeError: count(): Argument #1 ($var) must be of type Countable|array, bool given in C:\apache\htdocs\wordpress\wp-content\plugins\acf-field-block\includes\class-acf-field-block-renderer.php:385

The logic should take these instances into account and return early when there's nothing to render.

This test should be performed within the rendering method.