Removing all categories or tags from the sidebar won't save

[Canapin (Coin-coin le Canapin)]

Steps to reproduce:

1. Go to your sidebar preferences
   

   

2. Remove all categories and/or tags

3. Click Save Changes
   

   

4. Reload:
   

   

[mcwumbly (Dave McClure)]

see: Default tags appear in sidebar if user preference is empty