[SearchKit] Do not crash on entities without fields

[jensschuppe]

Overview

The SearchKit admin interface crashes when there are entities without fields (e.g. custom API entities not derived from DAOs).

Before

A custom API entity without any fields causes the SearchKit admin interface to crash with TypeError: array_reverse(): Argument #1 ($array) must be of type array, null given in array_reverse().

After

Entites without fields just don't have fields in SearchKit, no crashing.

Technical Details

There's an assumption that empty attributes for entities should not be part of the schema at all in \Civi\Search\Admin::getSchema(), but SearchKit relies on the attribute fields being there in \Civi\Search\Admin::addImplicitFKFields().

[civibot]

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