Minor change to resolution switch code, so that my work around what seems a bug in the mac version of irrlicht doesn't introduce issues where this bug doesn't manifest

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@5108 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/graphics/irr_driver.cpp

@@ -765,6 +765,11 @@ void IrrDriver::update(float dt)
         if (m_res_switching)    m_res_switching = false;
         else                    main_loop->abort();
     }
+    else if (m_res_switching)
+    {
+        m_res_switching = false;
+    }
+    
     World *world = World::getWorld();
     
     const bool inRace = world!=NULL;