notifications: Don't error when dismissing missing notifications

Fixes: #2468.

- Two browser tabs could be loaded with the interface and the same notification
could be dismissed twice. When dismissing the notification for the second time,
we currently throw a 404 error. Instead silently ignore the error.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Veiko Aasa <veiko17@disroot.org>

plinth/views.py

@@ -568,9 +568,8 @@ def notification_dismiss(request, id):
     """Dismiss a notification."""
     from .notification import Notification
     notes = Notification.list(key=id, user=request.user)
-    if not notes:
-        raise Http404
-
-    notes[0].dismiss()
+    if notes:
+        # If a notification is not found, no need to dismiss it.
+        notes[0].dismiss()
 
     return HttpResponseRedirect(_get_redirect_url_from_param(request))