KFontChooserDialog: handle dialog being deleted by parent during exec()
It had been discussed here before: https://phabricator.kde.org/D28122#inline-160325 but at that time was not handled or rather left as in the initial patch.
IMHO though if client code does create dialogs on the stack, their decision. We do a library here, and thus should do best practice and catch any possible crash. Besides, lots of other places in KF modules do such cautious handling, and things should follow a consistent policy. That policy had been ebn.kde.org/krazy which warned about that and thus people added the protection. We sadly lost that for now, hopefully some gitlab tooling will bring that back one day.