Disable copy construction of QObject subclasses

src/gui/previewselectdialog.h

@@ -48,6 +48,7 @@ class PreviewListDelegate;
 class PreviewSelectDialog final : public QDialog
 {
     Q_OBJECT
+    Q_DISABLE_COPY(PreviewSelectDialog)
 
 public:
     enum PreviewColumn

src/gui/rss/automatedrssdownloader.h

@@ -53,6 +53,7 @@ namespace Ui
 class AutomatedRssDownloader : public QDialog
 {
     Q_OBJECT
+    Q_DISABLE_COPY(AutomatedRssDownloader)
 
 public:
     explicit AutomatedRssDownloader(QWidget *parent = nullptr);