Correction to 8eb96b2d6: isHidden() is always 'false' (#4622)

Using \!isVisible() instead behaves as expected, to avoid updating elevation chart widget in training to be updating when it is not in the selected layout

src/Train/ElevationChartWindow.cpp

@@ -303,7 +303,7 @@ void
 ElevationChartWindow::telemetryUpdate(const RealtimeData &rtData)
 {
     // If it is not visible, it saves time
-    if (isHidden())
+    if (!isVisible())
         return;
     m_rtData = rtData;
     bubbleWidget->setRealtimeData(&m_rtData);