New function: Trigger error event

* VuFindSearch/Service.php (triggerError): New function. Trigger error
  event.

module/VuFindSearch/src/VuFindSearch/Service.php

@@ -267,6 +267,19 @@ class Service
         return $this->backends[$backend];
     }
 
+    /**
+     * Trigger the error event.
+     *
+     * @param BackendException $exception Error exception
+     * @param array            $args      Event arguments
+     *
+     * @return void
+     */
+    public function triggerError(BackendException $exception, $args)
+    {
+        $this->getEventManager()->trigger('error', $exception, $args);
+    }
+
     /**
      * Trigger the pre event.
      *