cstool: cs_op_count() can return -1. fix #978
cstool: cs_op_count() can return -1. fix #978

bSr43/capstone,bSr43/capstone,AmesianX/capstone,bSr43/capstone,bSr43/capstone,AmesianX/capstone,AmesianX/capstone,AmesianX/capstone,AmesianX/capstone,bSr43/capstone,bSr43/capstone,AmesianX/capstone,AmesianX/capstone,bSr43/capstone