net: remove another unguarded sysfile == nil check
net: remove another unguarded sysfile == nil check

Putting aside the unguarded access to fd.sysfile, the condition will never be true as fd.incref above handles the closed condition.

R=mikioh.mikioh, dvyukov
CC=golang-dev
http://codereview.appspot.com/6845062

tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,tv42/old-go,gnanderson/go,apparentlymart/golang,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang,gnanderson/go,tv42/old-go,dsriram/golang,gnanderson/go,gnanderson/go,tv42/old-go,dsriram/golang,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,gnanderson/go,dsriram/golang,gnanderson/go