fix an undefined integer overflow
fix an undefined integer overflow

natgla/csmith,jacekburys/csmith,Panos90/csmith,Panos90/csmith,DmitryOlshansky/dsmith,DmitryOlshansky/dsmith,DmitryOlshansky/dsmith,jacekburys/csmith,jacekburys/csmith,jacekburys/csmith,natgla/csmith,Panos90/csmith,natgla/csmith,natgla/csmith,Panos90/csmith,jacekburys/csmith,DmitryOlshansky/dsmith