Regression from MDL-81119

If forced config settings for backup and/or restore aren't set, storing or restoring an item from the recycle bin will temporarily set the forced config settings to null when attempting to restore the original settings.

This will cause a fatal error if get_config() is called on 'backup' or 'restore' after this.

I haven't seen this causing issues in a standalone backup or restore, but this is a standard combination so it could easily be breaking something.