Avoid adding duplicate menuitems (windows)

Previously, when calling `.SetHidden(false)` on a menu item that was not hidden, a duplicate menu item was created.

v3/examples/menu/main.go

@@ -46,7 +46,7 @@ func main() {
 
 	// Hidden menu item that can be unhidden
 	hidden := myMenu.Add("I was hidden").SetHidden(true)
-	myMenu.Add("Toggle hidden menu").OnClick(func(ctx *application.Context) {
+	myMenu.Add("Toggle the hidden menu").OnClick(func(ctx *application.Context) {
 		hidden.SetHidden(!hidden.Hidden())
 	})
 

v3/examples/systray-custom/main.go

@@ -2,11 +2,12 @@ package main
 
 import (
 	_ "embed"
+	"log"
+	"runtime"
+
 	"github.com/wailsapp/wails/v3/pkg/application"
 	"github.com/wailsapp/wails/v3/pkg/events"
 	"github.com/wailsapp/wails/v3/pkg/icons"
-	"log"
-	"runtime"
 )
 
 var windowShowing bool
@@ -52,6 +53,12 @@ func main() {
 
 	systemTray := app.NewSystemTray()
 	menu := app.NewMenu()
+	// Hidden menu item that can be unhidden
+	hidden := menu.Add("I was hidden").SetHidden(true)
+	menu.Add("Toggle the hidden menu").OnClick(func(ctx *application.Context) {
+		hidden.SetHidden(!hidden.Hidden())
+		menu.Update()
+	})
 	menu.Add("Quit").OnClick(func(data *application.Context) {
 		app.Quit()
 	})

v3/pkg/application/menuitem_windows.go

@@ -24,8 +24,8 @@ type windowsMenuItem struct {
 }
 
 func (m *windowsMenuItem) setHidden(hidden bool) {
-	m.hidden = hidden
-	if m.hidden {
+	if hidden && !m.hidden {
+		m.hidden = true
 		// iterate the parent items and find the menu item before us
 		for i, item := range m.parent.items {
 			if item == m.menuItem {
@@ -41,7 +41,8 @@ func (m *windowsMenuItem) setHidden(hidden bool) {
 		// m.pos = w32.GetMenuItemPosition(m.hMenu, uint32(m.id))
 		// Remove from parent menu
 		w32.RemoveMenu(m.hMenu, m.id, w32.MF_BYCOMMAND)
-	} else {
+	} else if !hidden && m.hidden {
+		m.hidden = false
 		// Add to parent menu
 		// Get the position of the item before us
 		var pos int