Add comments about the risk of dangling pointers

src/library/baseexternallibraryfeature.cpp

@@ -58,7 +58,8 @@ void BaseExternalLibraryFeature::onRightClick(const QPoint& globalPos) {
 
 void BaseExternalLibraryFeature::onRightClickChild(
         const QPoint& globalPos, const QModelIndex& index) {
-    //Save the model index so we can get it in the action slots...
+    // Save the model index so we can get it in the action slots...
+    // Make sure that this is reset when the related TreeItem is deleted.
     m_lastRightClickedIndex = index;
     QMenu menu(m_pSidebarWidget);
     menu.addAction(m_pAddToAutoDJAction);

src/library/baseexternallibraryfeature.h

@@ -54,6 +54,8 @@ class BaseExternalLibraryFeature : public LibraryFeature {
   private:
     void addToAutoDJ(PlaylistDAO::AutoDJSendLoc loc);
 
+    // Caution: Make sure this is reset whenever the library tree is updated,
+    // so that the internalPointer() does not become dangling
     QModelIndex m_lastRightClickedIndex;
 
     parented_ptr<QAction> m_pAddToAutoDJAction;

src/library/browse/browsefeature.cpp

@@ -273,6 +273,8 @@ void BrowseFeature::activateChild(const QModelIndex& index) {
 
 void BrowseFeature::onRightClickChild(const QPoint& globalPos, const QModelIndex& index) {
     TreeItem *item = static_cast<TreeItem*>(index.internalPointer());
+
+    // Make sure that this is reset when the related TreeItem is deleted.
     m_pLastRightClickedItem = item;
 
     if (!item) {

src/library/browse/browsefeature.h

@@ -70,6 +70,9 @@ class BrowseFeature : public LibraryFeature {
     QAction* m_pAddQuickLinkAction;
     QAction* m_pRemoveQuickLinkAction;
     QAction* m_pAddtoLibraryAction;
+
+    // Caution: Make sure this is reset whenever the library tree is updated,
+    // so that the internalPointer() does not become dangling
     TreeItem* m_pLastRightClickedItem;
     TreeItem* m_pQuickLinkItem;
     QStringList m_quickLinkList;