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/Input.cpp

@@ -492,6 +492,10 @@ static void menuactionpress(void)
             ed.getDirectoryData();
             game.loadcustomlevelstats(); //Should only load a file if it's needed
             game.createmenu(Menu::levellist);
+            if (FILESYSTEM_levelDirHasError())
+            {
+                game.createmenu(Menu::warninglevellist);
+            }
             map.nexttowercolour();
             break;
  #if !defined(NO_EDITOR)
@@ -1728,6 +1732,7 @@ static void menuactionpress(void)
         map.nexttowercolour();
         break;
     case Menu::errorloadinglevel:
+    case Menu::warninglevellist:
         music.playef(11);
         game.returnmenu();
         map.nexttowercolour();