Ordering shouldn't matter when specify field numbers

[uluyol]

If I have the following test:

type TestMesg struct {
	F1 string            `protobuf:"1,opt"`
	F2 int32             `protobuf:"10,opt"`
	F4 []byte            `protobuf:"99,opt"`
	F3 protobuf.Ufixed64 `protobuf:"14,opt"`
	F5 float64           `protobuf:"108,opt"`
}

func TestEncodeRoundTrip(t *testing.T) {
	m := TestMesg{
		F1: "abasdfasdf312123",
		F2: 109,
		F3: protobuf.Ufixed64(^uint64(0)),
		F4: []byte{0, 12, 44},
		F5: 505.5,
	}

	buf, err := protobuf.Encode(&m)
	if err != nil {
		t.Errorf("unable to encode")
	}

	var m2 TestMesg
	if err := protobuf.Decode(buf, &m2); err != nil {
		t.Errorf("unable to decode")
	}

	if !reflect.DeepEqual(&m, &m2) {
		t.Errorf("written and read msg differ:\nhave %+v\nwant %+v", &m2, &m)
	}
}

Running it fails with

--- FAIL: TestEncodeRoundTrip (0.00s)
	pb_test.go:38: written and read msg differ:
		have &{F1:abasdfasdf312123 F2:109 F4:[0 12 44] F3:0 F5:505.5}
		want &{F1:abasdfasdf312123 F2:109 F4:[0 12 44] F3:18446744073709551615 F5:505.5}

But if I switch the order of F3 and F4 then it passes.