Fix ARGState.getEdgeToChild that was changed by bamRecursion branch.
If there exists a regular edge to a child,
we want to return that edge.
The summary edge should only be returned as a backup
if no other edge exists.
The current code breaks -skipRecursion is used,
because in this case we have a summary edge and a regular edge
between the same two locations.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13942 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c