Fix color picker dismissed callback

[ole108]

Description:

Call the callback provided to the color picker dialog with a nil color if the dialog is dismissed.
So users can easily distinguish between confirmation and dismissal and react to it.
This is inline with how all the file related dialogs work (fileSave, fileOpen and folderOpen).

Fixes #5237

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

Where applicable:

[andydotxyz]

I would prefer that we match the data input dialogs not the file dialogs.
I thought the bug you reported was that the close and callback were not called in the right order?

[ole108]

I didn't look at the data input dialogs at all yet.
That's next.
Other order of close and callback would fix it, too.
I can dig into that. I suggest that both would be best.

[andydotxyz]

The trouble with adding a "callback(nil)" to all dialogs is that some are picking an item that has a valid zero value.
i.e. Entry with a string may allow empty string which should not be accidentally confused with cancel.

The File dialog "calls nil on cancel" was added before the SetOnClosed was added. Maybe it shouldn't be there at all?

[ole108]

OK. I will look into the order of callbacks tomorrow.
That would work for me, too.
And consistency would be great.
I might have started my Fyne journey at the wrong end. 🤷

[ole108]

I updated the PR with the correct callback order.
I hope this is good now.

[andydotxyz]

The change of order seems reasonable, but the adding of possible panics worries me.

[andydotxyz]

I have looked into this to approve and only just realised (sorry if there was a discussion before) that this makes the close order different for the colour picker than for all others.
I agree that the change makes sense, but probably it needs to apply to dialog/base.go:101 as well so that dialogs that use the builtin callback get data before dismissal.

It could be checked by using the other data input dialogs (Form, Entry) in the context of your dialog library to see if you get data from either of those.