Fixed an (harmless) error message that was printed on the console

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@4335 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/states_screens/challenges.cpp

@@ -81,7 +81,7 @@ namespace GUIEngine
         for (int n=0; n<lockedChallengeAmount; n++)
         {
             w->addItem( _("Locked : solve active challenges to gain access to more!"), "locked",
-                       file_manager->getGUIDir() + "/challenge.png", true);
+                       "/gui/challenge.png", true);
             std::cout << "// Adding locked challenge <" << lockedChallenges[n]->getId().c_str() << ">\n";
 
         }