net/http: query values from r.PostForm first in *Request.FormValue

As the doc of http.Request.FormValue says:
"POST, PUT, and PATCH body parameters take precedence over URL query string
values".

So query values from r.PostForm first.

Fixes #64575

src/net/http/request.go

@@ -1374,6 +1374,9 @@ func (r *Request) FormValue(key string) string {
 	if r.Form == nil {
 		r.ParseMultipartForm(defaultMaxMemory)
 	}
+	if vs := r.PostForm[key]; len(vs) > 0 {
+		return vs[0]
+	}
 	if vs := r.Form[key]; len(vs) > 0 {
 		return vs[0]
 	}

src/net/http/request_test.go

@@ -52,8 +52,8 @@ func TestParseFormSemicolonSeparator(t *testing.T) {
 }
 
 func TestParseFormQuery(t *testing.T) {
-	req, _ := NewRequest("POST", "http://www.google.com/search?q=foo&q=bar&both=x&prio=1&orphan=nope&empty=not",
-		strings.NewReader("z=post&both=y&prio=2&=nokey&orphan&empty=&"))
+	req, _ := NewRequest("POST", "http://www.google.com/search?q=foo&q=bar&both=x&prio=1&orphan=nope&empty=not&dup=url",
+		strings.NewReader("z=post&both=y&prio=2&=nokey&orphan&empty=&dup=body&"))
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded; param=value")
 
 	if q := req.FormValue("q"); q != "foo" {
@@ -77,6 +77,9 @@ func TestParseFormQuery(t *testing.T) {
 	if prio := req.FormValue("prio"); prio != "2" {
 		t.Errorf(`req.FormValue("prio") = %q, want "2" (from body)`, prio)
 	}
+	if dup := req.FormValue("dup"); dup != "body" {
+		t.Errorf(`req.FormValue("dup") = %q, want "body" (from body)`, dup)
+	}
 	if orphan := req.Form["orphan"]; !reflect.DeepEqual(orphan, []string{"", "nope"}) {
 		t.Errorf(`req.FormValue("orphan") = %q, want "" (from body)`, orphan)
 	}