Deleting a task will break the widget for users with saved progress

If a user has saved progress for a task which doesn't exist, then the widget will break with an error.

Workaround is to clear the localStorage, to get rid of that non-existent key.

Steps to reproduce:

1. Log in as a user, and skip any task (so the progress is saved in localStorage)
2. Delete a task
3. As that same user, the GuidedTour widget is now broken.