Server: Fix --serverinfo country code misinterpretation on Qt6

[hoffie]

Short description of changes

• Util: Make CLocale::IsCountryCodeSupported more robust

  On Qt6, we previously relied on the caller to only supply country codes within bounds. With this change we properly check before risking an uninitialized array access.

  On Qt5, we did not do any checks at all. Now we ensure that we what is provided is a valid Qt5 country code.

• Server: Fix --serverinfo country code misinterpretation on Qt6

  Previously, country codes in --serverinfo were interpreted natively.
  This worked for Qt5, but caused unintended changes on Qt6 builds as the codes differ. Not doing a conversion for --serverinfo was an oversight from the initial Qt6 compatibility work, which is now fixed with this change.

CHANGELOG: Server: Fixed --serverinfo country code misinterpretation introduced in Jamulus 3.9.0 on Qt6-based builds such as Mac

Context: Fixes an issue?

Related: #2299
Fixes: #2809

Does this change need documentation? What needs to be documented and how?

• Release announcement (reminder in Prepare Release 3.9.1 #2813)

Status of this Pull Request

Ready. Tested both on Qt5 and Qt6. Qt6 builds with this change behave like Qt5 builds again.

What is missing until this pull request can be merged?
Reviews.

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want
• My code follows the style guide
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• I've filled all the content above

[hoffie]

@acerix Could you please try a build from this PR and confirm if it works as expected with your original, pre-3.9.0 --serverinfo line?

[acerix]

@acerix Could you please try a build from this PR and confirm if it works as expected with your original, pre-3.9.0 --serverinfo line?

I can confirm this PR reverts back to my previous "38: Canada" setting with 3.8 and Qt5.

Thanks @hoffie for the astounding support.

[pljones]

@hoffie can you pick this up?

[ann0see]

Tested on macOS and it's ok. Thanks!

[hoffie]

Removing needs documentation tag as the reminder has been added to #2813.

[pljones]

Removing needs documentation tag as the reminder has been added to #2813.

Can you get an issue raised, too, please (and added to the board).

[hoffie]

Can you get an issue raised, too, please (and added to the board).

Hm? We have collected all pre-known release announcement items right in the existing 3.9.1 tracker #2813. I have added this PR there (that's what I meant above). Do you want a separate issue for the sub-task (write the release announcement) or even for each sub-item? We didn't have that until now.

[pljones]

No - but if documentation needs updating, there will be a pull request. I like an issue for each pull request, so the pull request isn't just "floating".

[hoffie]

No - but if documentation needs updating, there will be a pull request. I like an issue for each pull request, so the pull request isn't just "floating".

As far as I can see, we won't need to update existing documentation on the website for this issue (Qt6 bugfix). I had added the label as a reminder for the release announcement and have now removed it as it is properly tracked.
Did you mean to comment on #2841?

[pljones]

Ah right, if it was just for the release announcement, then so long as there's a reminder there, then "done".