Make connection unique for annotation visibility actions

This event is sent three times at startup and two times per tab at tab
change, so let's make sure we setup the connections only once.

ui/annotationactionhandler.cpp

@@ -715,8 +715,8 @@ void AnnotationActionHandler::setupAnnotationToolBarVisibilityAction()
     Q_ASSERT(itToolBar != toolbars.end());
     KToolBar *annotationToolBar = mw->toolBar(QStringLiteral("annotationToolBar"));
     d->aShowToolBar->setChecked(annotationToolBar->isVisible());
-    connect(annotationToolBar, &QToolBar::visibilityChanged, d->aShowToolBar, &QAction::setChecked);
-    connect(d->aShowToolBar, &QAction::toggled, annotationToolBar, &KToolBar::setVisible);
+    connect(annotationToolBar, &QToolBar::visibilityChanged, d->aShowToolBar, &QAction::setChecked, Qt::UniqueConnection);
+    connect(d->aShowToolBar, &QAction::toggled, annotationToolBar, &KToolBar::setVisible, Qt::UniqueConnection);
     connect(d->aShowToolBar, &QAction::toggled, this, [this](bool checked) { d->slotToolBarVisibilityChanged(checked); });
 }