Fix bug in KqueuePollster.register_writer().
Fix bug in KqueuePollster.register_writer().

1st1/asyncio,jashandeep-sohi/asyncio,jashandeep-sohi/asyncio,haypo/trollius,manipopopo/asyncio,gsb-eng/asyncio,gvanrossum/asyncio,manipopopo/asyncio,Martiusweb/asyncio,fallen/asyncio,1st1/asyncio,vxgmichel/asyncio,haypo/trollius,ajdavis/asyncio,fallen/asyncio,gsb-eng/asyncio,manipopopo/asyncio,fallen/asyncio,Martiusweb/asyncio,gsb-eng/asyncio,ajdavis/asyncio,vxgmichel/asyncio,ajdavis/asyncio,vxgmichel/asyncio,gvanrossum/asyncio,haypo/trollius,Martiusweb/asyncio,gvanrossum/asyncio,jashandeep-sohi/asyncio,1st1/asyncio