runtime: fix potential deadlock in netpoll on windows If netpoll has been told to block, it must not return with nil, otherwise scheduler assumes that netpoll is disabled.
runtime: fix potential deadlock in netpoll on windows
If netpoll has been told to block, it must not return with nil,
otherwise scheduler assumes that netpoll is disabled.

R=golang-dev, alex.brainman
CC=golang-dev
https://codereview.appspot.com/11920044

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