Don't try to retranslate strings for native color dialogs

If the native color dialog is in use we haven't created any of the
widgets and will crash when trying to update them.

Change-Id: I6c43cc47359110c3b9db7cacb62581446cc6f7a3
Fixes: QTBUG-75858
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/widgets/dialogs/qcolordialog.cpp

@@ -1858,6 +1858,9 @@ void QColorDialogPrivate::_q_addCustom()
 
 void QColorDialogPrivate::retranslateStrings()
 {
+    if (nativeDialogInUse)
+        return;
+
     if (!smallDisplay) {
         lblBasicColors->setText(QColorDialog::tr("&Basic colors"));
         lblCustomColors->setText(QColorDialog::tr("&Custom colors"));