Fix proposal for unsoundness issue #13 + test case

This patch addresses the unsoundness issue #13. The idea is to first collect the UB constraints and then add them together with the Phi node predicates. If no Phi nodes exist, add the UB constraints directly as instruction conditions. The recursive parsing at each Phi node can be improved, but we should discuss the proposed solution first.
If I see it correctly, we have the same situation as for the case above where we have to constrain predicates after index ```A```: For any upcoming, i.e., surrounding phi's, the corresponding path predicate must be added to the UB condition.