Fix for boolean type error in $this->entity->hasField

When calling the ListIdentifiers or ListRecords verbs, if a node is unable to be accessed (for example, if it is not assigned to the current domain) $this->entity is set to the value 'false', and a type error is thrown when it attempts to call $this->entity->hasField. This code change checks if $this->entity is false after the call to loadEntity, and continues to the next entity if it is.