[grpc-go] time-sequence of recv ands.cancel by timeout server-stream client

[Zeymo Wang]

Server-stream client  which `mc.Timeout > 0` , accompanied by `tailer` (status and message) coming, frame reader will finsh stream and invoke s.canel() which pass by context.WithTimout(ctx,mc.Timeout),but caller maybe reading data in `receiveBufferReader`  will return err as `context cancel` and break `Recv()` .How dose timeout client guarantee two operation in correct time-sequence?