Always reparent start dialog windows on macOS

Because not doing so crashes on Qt6. It's the inverse of Linux on Qt6,
which crashes when reparenting instead, which is why this whole
rigmarole was added.

src/desktop/mainwindow.cpp

@@ -1535,6 +1535,13 @@ void MainWindow::setStartDialogActions(dialogs::StartDialog *dlg)
 
 void MainWindow::closeStartDialog(dialogs::StartDialog *dlg, bool reparent)
 {
+	// Linux on Qt6 crashes when reparenting children of a dialog that's about
+	// to close after hosting, so we don't reparent in that case and just close
+	// the dialog. On the other hand, macOS on Qt6 crashes when closing the
+	// dialog instead, so we always reparent there.
+#ifdef Q_OS_MACOS
+	reparent = true;
+#endif
 	if(reparent) {
 		for(QDialog *child : dlg->findChildren<QDialog *>(
 				QString(), Qt::FindDirectChildrenOnly)) {