Display improper zip structure message to non-console users

If a zip file is improperly structured, a message will be displayed when
the player loads the level list.

This will only display the last-displayed improper zip, because there
only needs to be one displayed at a time. Also because doing anything
more would most likely require heap allocation, and I don't want to do
that.

desktop_version/src/Game.cpp

@@ -6478,7 +6478,9 @@ void Game::createmenu( enum Menu::MenuName t, bool samemenu/*= false*/ )
         menuyoff = 10;
         break;
     case Menu::errorloadinglevel:
+    case Menu::warninglevellist:
         option("ok");
+        menuyoff = 50;
         break;
     }