Don't crash if energy measurement was not started.
Don't crash if energy measurement was not started.

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