Fix guard clause in WebPushNotificationWorker (#4421)

app/workers/web_push_notification_worker.rb

@@ -9,16 +9,17 @@ class WebPushNotificationWorker
     session_activation = SessionActivation.find(session_activation_id)
     notification       = Notification.find(notification_id)
 
-    return if session_activation.nil? || notification.nil?
+    return if session_activation.web_push_subscription.nil? || notification.activity.nil?
 
-    begin
     session_activation.web_push_subscription.push(notification)
-    rescue Webpush::InvalidSubscription, Webpush::ExpiredSubscription => e
+  rescue Webpush::InvalidSubscription, Webpush::ExpiredSubscription
     # Subscription expiration is not currently implemented in any browser
+
     session_activation.web_push_subscription.destroy!
     session_activation.update!(web_push_subscription: nil)
 
-      raise e
-    end
+    true
+  rescue ActiveRecord::RecordNotFound
+    true
   end
 end