Error when removing all Widgets

[fitztrev]

After disabling all Widgets and saving, the following error occurs:

Warning: array_values() [function.array-values]:
The argument should be an array in /var/www/trunk/wp-admin/widgets.php on line 78

To recreate:

1) Enable some widgets, if not done already.

2) Disable each of them

3) Save changes

[darkdragon]

Duplicate of #2784

Fix is part of patch.