fix crash if cpu-energy-meter is not available
fix crash if cpu-energy-meter is not available

sosy-lab/benchexec,ultimate-pa/benchexec,dbeyer/benchexec,IljaZakharov/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,IljaZakharov/benchexec,martin-neuhaeusser/benchexec,dbeyer/benchexec,sosy-lab/benchexec,martin-neuhaeusser/benchexec,martin-neuhaeusser/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,IljaZakharov/benchexec,martin-neuhaeusser/benchexec,sosy-lab/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,dbeyer/benchexec,dbeyer/benchexec,sosy-lab/benchexec,IljaZakharov/benchexec,ultimate-pa/benchexec