FileDialog.SetOnClosed not always working

[codesoap]

Checklist

• I have searched the issue tracker for open issues that relate to the same problem, before opening a new one.
• This issue only relates to a single bug. I will open new issues for any other problems.

Describe the bug

If SetOnClosed is called on a FileDialog before Show is called, the callback will not be called when the dialog is closed.

How to reproduce

Run the example code, close the file dialog and see that foo is not printed to standard output.

Screenshots

No response

Example code

package main

import "fyne.io/fyne/v2"
import "fyne.io/fyne/v2/app"
import "fyne.io/fyne/v2/dialog"

func main() {
	a := app.New()
	w := a.NewWindow("test")

	fd := dialog.NewFileOpen(func(rc fyne.URIReadCloser, err error) {}, w)
	fd.SetOnClosed(func() { println("foo") })
	fd.Show()

	w.ShowAndRun()
}

Fyne version

2.4.4

Go compiler version

1.22.0

Operating system and version

MX Linux, I believe version 21; it's basically Debian

Additional Information

It works, if SetOnClosed is called after Show:

package main

import "fyne.io/fyne/v2"
import "fyne.io/fyne/v2/app"
import "fyne.io/fyne/v2/dialog"

func main() {
	a := app.New()
	w := a.NewWindow("test")

	fd := dialog.NewFileOpen(func(rc fyne.URIReadCloser, err error) {}, w)
	fd.Show()
	fd.SetOnClosed(func() { println("foo") })

	w.ShowAndRun()
}

The problem seems to be that f.dialog == nil is checked in SetOnClosed, but f.dialog is only set once Show is called.

My initial impulse was to just remove the early return in SetOnClosed, but I suppose it's there for a reason (which I don't see right now), so I didn''t open a PR.

[codesoap]

It just occurred to me, that the check should probably be run within the callback, so I created #4652 .

[codesoap]

Closing, because #4652 has been merged.