fix config: when setting a soft threshold, also set a hard threshold, because softThreshold=0 and hardThreshold=-1 is the same as the standard configuration, plus extra effort without any effects

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14840 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c