fixes possible call to pthread_kill on negative ids (which may lead to killing the xserver and other applications)
fixes possible call to pthread_kill on negative ids (which may lead to killing the xserver and other applications)

finnhaedicke/metaSMT,hoangmle/metaSMT,hoangmle/metaSMT,agra-uni-bremen/metaSMT,finnhaedicke/metaSMT,finnhaedicke/metaSMT,nbruns1/metaSMT,nbruns1/metaSMT,agra-uni-bremen/metaSMT,hoangmle/metaSMT,agra-uni-bremen/metaSMT,nbruns1/metaSMT