Logic issue with selected attributes

When you have a selected attributes not allowed _uc_dependent_attributes_filter doesn't work well because it ends in both cases:
1. there are no more descendant
2. it breaks when a selected attribute is not allowed (eg when selection defaults to a value not allowed)

I send a patch which solves this problem.
I hope someone else will test it.

P.S. Currently this module works as expected only if uc_aac has:
1. "Ajax Attribute Calculations dynamically adjusts product information as a product's attribute options are changed." Enabled
2. Display price adjustment selected
in admin/store/settings/attributes

Cheers