xml: fix reflect error

Fixes #1749.

R=bradfitz
CC=golang-dev
https://golang.org/cl/4431075

src/pkg/xml/read.go

@@ -220,13 +220,10 @@ func (p *Parser) unmarshal(val reflect.Value, start *StartElement) os.Error {
 	}
 
 	if pv := val; pv.Kind() == reflect.Ptr {
-		if pv.Pointer() == 0 {
-			zv := reflect.Zero(pv.Type().Elem())
-			pv.Set(zv.Addr())
-			val = zv
-		} else {
-			val = pv.Elem()
+		if pv.IsNil() {
+			pv.Set(reflect.New(pv.Type().Elem()))
 		}
+		val = pv.Elem()
 	}
 
 	var (

src/pkg/xml/xml_test.go

@@ -347,6 +347,7 @@ type allScalars struct {
 	Float32   float32
 	Float64   float64
 	String    string
+	PtrString *string
 }
 
 var all = allScalars{
@@ -368,8 +369,11 @@ var all = allScalars{
 	Float32:   13.0,
 	Float64:   14.0,
 	String:    "15",
+	PtrString: &sixteen,
 }
 
+var sixteen = "16"
+
 const testScalarsInput = `<allscalars>
 	<true1>true</true1>
 	<true2>1</true2>
@@ -390,6 +394,7 @@ const testScalarsInput = `<allscalars>
 	<float32>13.0</float32>
 	<float64>14.0</float64>
 	<string>15</string>
+	<ptrstring>16</ptrstring>
 </allscalars>`
 
 func TestAllScalars(t *testing.T) {
@@ -401,7 +406,7 @@ func TestAllScalars(t *testing.T) {
 		t.Fatal(err)
 	}
 	if !reflect.DeepEqual(a, all) {
-		t.Errorf("expected %+v got %+v", all, a)
+		t.Errorf("have %+v want %+v", a, all)
 	}
 }