Improve the handling of MultiEdges in the AutomatonCPA.
If the transition conditions for an edge inside a MultiEdge
could not be fully evaluated (because they rely on other CPAs),
we stay in the current state instead of going to TOP immediately.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14169 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c