cleanup and fix bug

GUI/View/Scene/MaskGraphicsScene.cpp

@@ -338,7 +338,7 @@ void MaskGraphicsScene::updateOverlays()
         }
     }
 
-    // update Z-values of all IMaskView to reflect stacking order
+    // update Z-values of all overlays to reflect stacking order
     int z = 0;
     for (const MaskItem* maskItem : *m_masks) {
         if (IOverlay* overlay = m_mask2overlay[maskItem])
@@ -534,7 +534,7 @@ void MaskGraphicsScene::onSceneSelectionChanged()
 
     if (!selectedMaskOverlay()) {
         // if mask is not selected because it was hidden, do not switch Set to unselected state
-        if (m_masks->currentItem()->isVisible())
+        if (m_masks->currentItem() && m_masks->currentItem()->isVisible())
             m_masks->setCurrentIndex(-1);
         m_prjns->setCurrentIndex(-1);
     } else {