buf fix: make FD.Read, FD.Write work for empty buffers
buf fix: make FD.Read, FD.Write work for empty buffers

R=r
DELTA=8  (6 added, 0 deleted, 2 changed)
OCL=19273
CL=19275

tv42/old-go,firebitsbr/golang-old,h8liu/golang,nightlyone/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,apparentlymart/golang,bdwalton/debian-golang,pombredanne/go-deleteme,pombredanne/go-deleteme,wesolows/golang,wesolows/golang,ssrl/go,ssrl/go,gnanderson/go,dsriram/golang,wesolows/golang,tv42/old-go,firebitsbr/golang-old,firebitsbr/golang-old,dsriram/golang,nightlyone/golang,tianon/debian-golang,pombredanne/go-deleteme,tv42/old-go,wesolows/golang,wesolows/golang-old,dsriram/golang,h8liu/golang,tianon/debian-golang,tianon/debian-golang,bdwalton/debian-golang,bdwalton/debian-golang,h8liu/golang,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,firebitsbr/golang-old,gnanderson/go,firebitsbr/golang-old,ssrl/go,tianon/debian-golang,dsriram/golang,wesolows/golang-old,pombredanne/go-deleteme,wesolows/golang-old,wesolows/golang-old,apparentlymart/golang,h8liu/golang,tianon/debian-golang,gnanderson/go,firebitsbr/golang-old,wesolows/golang,bdwalton/debian-golang,dsriram/golang,nightlyone/golang,bdwalton/debian-golang,pombredanne/go-deleteme,gnanderson/go,ssrl/go,tianon/debian-golang,h8liu/golang,nightlyone/golang,firebitsbr/golang-old,nightlyone/golang,bdwalton/debian-golang,dsriram/golang,pombredanne/go-deleteme,nightlyone/golang,wesolows/golang-old,h8liu/golang,apparentlymart/golang,tv42/old-go,ssrl/go,tv42/old-go,wesolows/golang-old,apparentlymart/golang,ssrl/go,wesolows/golang,dsriram/golang,nightlyone/golang,ssrl/go,bdwalton/debian-golang,tianon/debian-golang,apparentlymart/golang,tv42/old-go,tianon/debian-golang,firebitsbr/golang-old,gnanderson/go,wesolows/golang-old,wesolows/golang,h8liu/golang,bdwalton/debian-golang