Clicking "back to parent task" on subtask when parent has been deleted crashes the app
* create task for today
* create subtask
* drag subtask do tomorrow
* delete parent task
* go to the subtask (still present for tomorrow)
* click on "back to the parent task"
The app will crash.
Expected behavior: no "back to the parent task" link, since the task has been orphaned during the deletion of the parent.