do not show context menu if FitParameterWidget has no contents

GUI/View/Fit/FitParameterWidget.cpp

@@ -136,6 +136,9 @@ void FitParameterWidget::onFitParameterTreeContextMenu(const QPoint& point)
         setActionsEnabled(false);
         return;
     }
+    if (jobItem()->fitParameterContainerItem()->isEmpty())
+        return;
+
     QMenu menu;
     menu.addAction(m_removeFitParAction);
     menu.exec(m_treeView->viewport()->mapToGlobal(point));