fix NPE

Author: kmvi

mangadownloader/forms/frmMain.pas

@@ -3540,7 +3540,7 @@ procedure TMainForm.pmFavoritesPopup(Sender: TObject);
     miFavoritesEnable.Enabled := iEnable;
     miFavoritesDisable.Enabled := iDisable;
     miFavoritesTransferWebsite.Enabled := True;
-    if vtFavorites.SelectedCount = 1 then
+    if (vtFavorites.SelectedCount = 1) and Assigned(vtFavorites.FocusedNode) then
     begin
       miFavoritesViewInfos.Enabled := True;
       miFavoritesDownloadAll.Enabled := (Trim(FavoriteManager[vtFavorites.FocusedNode^.Index].FavoriteInfo.Link) <> '');