remove 3D view along with sample

GUI/View/SampleDesigner/SampleView.cpp

@@ -116,8 +116,10 @@ void SampleView::updateSingleSampleMode()
 
 void SampleView::onRequestViewInRealspace(Item3D* item)
 {
-    if (!item)
+    if (!item) {
+        m_realspacePanel->widget()->clearDisplay();
         return;
+    }
 
     m_docks->setDockVisible(REALSPACEPANEL);
     m_realspacePanel->widget()->setDisplayedItem(m_sampleSelectionView->currentSample(), item);

GUI/View/SampleView/RealspaceWidget.h

@@ -35,6 +35,7 @@ public:
     ~RealspaceWidget() override;
 
     void setDisplayedItem(MultiLayerItem* containingMultiLayerItem, Item3D* item);
+    void clearDisplay() { setDisplayedItem(nullptr, nullptr); }
     void defaultView();
     void sideView();
     void topView();