buffer: do not allocate background buffer until it's needed

Author: vmg

buffer.go

@@ -36,11 +36,10 @@ type buffer struct {
 // newBuffer allocates and returns a new buffer.
 func newBuffer(nc net.Conn) buffer {
 	fg := make([]byte, defaultBufSize)
-	bg := make([]byte, defaultBufSize)
 	return buffer{
 		buf:  fg,
 		nc:   nc,
-		dbuf: [2][]byte{fg, bg},
+		dbuf: [2][]byte{fg, nil},
 	}
 }