set dangling pointer to 0 so if a proxymodel gets called during resetting, it can tell if a plitem is gone

src/libtomahawk/playlist/playlistmodel.cpp

@@ -145,6 +145,7 @@ PlaylistModel::clear()
     {
         emit beginResetModel();
         delete m_rootItem;
+        m_rootItem = 0;
         emit endResetModel();
         m_rootItem = new PlItem( 0, this );
     }

src/libtomahawk/playlist/playlistmodel.h

@@ -51,7 +51,7 @@ public:
 
     Tomahawk::playlist_ptr playlist() const { return m_playlist; }
 
-    void loadPlaylist( const Tomahawk::playlist_ptr& playlist, bool loadEntries = true );
+    virtual void loadPlaylist( const Tomahawk::playlist_ptr& playlist, bool loadEntries = true );
     void loadHistory( const Tomahawk::source_ptr& source, unsigned int amount = 50 );
 
     void clear();