[BUG] Pushing 'w' to go to the next node to review throws an excessive error when the node has been deleted

[acardona]

Part of the problem is that deleting and adding nodes isn't notified to the Review widget, but solving that would take quite some effort.

Instead, just show an non-invasive notification that the node doesn't exist and move on. The error is massive and sends the message that something is broken, when it isn't:

Unsuccessful request: {"error": "No Treenode matches the given query.", "detail": "Traceback (most recent call last):\n File \"/opt/catmaid/fibsem/django/applications/catmaid/control/node.py\", line 2817, in update_location_reviewer\n r = Review.objects.get(treenode_id=node_id, reviewer=request.user)\n File \"/opt/catmaid/fibsem/django/env/lib/python3.8/site-packages/django/db/models/manager.py\", line 85, in manager_method\n return getattr(self.get_queryset(), name)(*args, **kwargs)\n File \"/opt/catmaid/fibsem/django/env/lib/python3.8/site-packages/django/db/models/query.py\", line 435, in get\n raise self.model.DoesNotExist(\ncatmaid.models.Review.DoesNotExist: Review matching query does not exist.\n\nDuring handling of the above exception, another exception occurred:\n\nTraceback (most recent call last):\n File \"/opt/catmaid/fibsem/django/env/lib/python3.8/site-packages/django/shortcuts.py\", line 76, in get_object_or_404\n return queryset.get(*args, **kwargs)\n File \"/opt/catmaid/fibsem/django/env/lib/python3.8/site-packages/django/db/models/query.py\", line 435, in get\n raise self.model.DoesNotExist(\ncatmaid.models.Treenode.DoesNotExist: Treenode matching query does not exist.\n\nDuring handling of the above exception, another exception occurred:\n\nTraceback (most recent call last):\n File \"/opt/catmaid/fibsem/django/env/lib/python3.8/site-packages/django/core/handlers/base.py\", line 181, in _get_response\n response = wrapped_callback(request, *callback_args, **callback_kwargs)\n File \"/usr/lib/python3.8/contextlib.py\", line 75, in inner\n return func(*args, **kwds)\n File \"/opt/catmaid/fibsem/django/applications/catmaid/history.py\", line 69, in wrapped_f\n result = f(*args, **kwargs)\n File \"/opt/catmaid/fibsem/django/applications/catmaid/control/authentication.py\", line 235, in inner_decorator\n return f(request, *args, **kwargs)\n File \"/opt/catmaid/fibsem/django/applications/catmaid/control/node.py\", line 2819, in update_location_reviewer\n node = get_object_or_404(Treenode, pk=node_id)\n File \"/opt/catmaid/fibsem/django/env/lib/python3.8/site-packages/django/shortcuts.py\", line 78, in get_object_or_404\n raise Http404('No %s matches the given query.' % queryset.model._meta.object_name)\ndjango.http.response.Http404: No Treenode matches the given query.\n", "type": "Http404", "meta": null}```