Issue #3527930: Guard entity rendering against TypeError in fullEntityCheck()

Wrap the render-to-markdown block in a try/catch(\Throwable) so that a single entity with corrupt field data (e.g. a taxonomy term with a NULL title causing Html::escape(null) → TypeError) no longer crashes the entire search response. On failure, a watchdog warning is logged (entity type, ID, message) and the loop continues with the remaining entities.