Fix cases where one edge too many was taken from an ARGPath
(the last edge of an ARGPath is actually beyond the last state
und mostly irrelevant).
This fixes for example the superfluous last edge
in the ErrorPath.*.txt output files.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13155 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c