Pass the on_result argument to the parent FileDialog constructors

[browniebroke]

I was trying to use the on_result argument for the self.main_window.select_folder_dialog(...) method and I my callback wasn't called. I looked at the code and noticed that some arguments added in #1464 were not being passed to the parent constructor.

I'm not sure if there is a particular reason for it, or if it was just missed. If the callback shouldn't be used, maybe it should be dropped from the docs.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

Thanks for the report and fix. FWIW, I think this is oversight/copy&paste error; the on_result handler is passed through on Windows and GTK. It wasn't picked up in previous testing because all the example code uses the await form of result handling.

You've marked the PR as draft; is there something you're planning to add or change in this PR? The only thing I can think you could add would be a testbed test, but that's definitely on the hard end. If you're up for a challenge, we'd love to have a testbed test of dialogs, but I can't point you at an existing example.

[browniebroke]

Thanks for the prompt response. The PR was marked as draft as I wanted to check that CI passed and that I covered everything, including tests. I tried to look at the existing testbed tests and it does indeed sound a bit too tricky to incorporate dialog, so I'll leave it as is.

I didn't realise that I could get to the result using await, that seems like a nicer way of doing it actually.

[freakboy3742]

I've made a small tweak to the release note, but otherwise this is good to go. Thanks for the PR!