msgbox: calling init func twice causes unexpected behavior

[gucio321]

to reproduce:

package main

import (
        "fmt"

        "github.com/AllenDang/giu"
)

func loop() {
        giu.Window("window").Layout(
                giu.PrepareMsgbox(),
                giu.PrepareMsgbox(),
                giu.Button("click me to see message box").OnClick(func() {
                        giu.Msgbox("Info", "I'm a msgbox. press OK to close me")
                }),
                giu.Button("show yes-no dialog").OnClick(func() {
                        giu.Msgbox("Question", "I'm yes-no dialog. Please take an action").
                                Buttons(giu.MsgboxButtonsYesNo).
                                ResultCallback(func(result giu.DialogResult) {
                                        switch result {
                                        case giu.DialogResultYes:
                                                fmt.Println("Yes clicked")
                                        case giu.DialogResultNo:
                                                fmt.Println("No clicked")
                                        }
                                })
                }),
                giu.Button("show ok-cancel dialog").OnClick(func() {
                        giu.Msgbox("ok-cancel", "I'm ok-cancel dialog").Buttons(giu.MsgboxButtonsOkCancel)
                }),
        )
}

func main() {
        wnd := giu.NewMasterWindow("Msg box demo", 640, 480, 0)
        wnd.Run(loop)
}

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