io.backend.unix: fix handle-length on stdin.
io.backend.unix: fix handle-length on stdin.

tgunr/factor,bpollack/factor,bpollack/factor,factor/factor,tgunr/factor,factor/factor,factor/factor,bpollack/factor,AlexIljin/factor,factor/factor,bpollack/factor,tgunr/factor,AlexIljin/factor,factor/factor,AlexIljin/factor,mrjbq7/factor,mrjbq7/factor,AlexIljin/factor,mrjbq7/factor,bpollack/factor,tgunr/factor,tgunr/factor,mrjbq7/factor,factor/factor,AlexIljin/factor,bpollack/factor,AlexIljin/factor,AlexIljin/factor,mrjbq7/factor,mrjbq7/factor,tgunr/factor,bpollack/factor