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.h

@@ -36,6 +36,7 @@ namespace Menu
         errornostart,
         errorsavingsettings,
         errorloadinglevel,
+        warninglevellist,
         graphicoptions,
         ed_settings,
         ed_desc,