Prevent players that have confirmed a kart selection from leaving game

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/branches/irrlicht@4267 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/states_screens/kart_selection.cpp

@@ -781,6 +781,13 @@ bool KartSelectionScreen::playerQuit(ActivePlayer* player)
     {
         if (m_kart_widgets[n].getAssociatedPlayer() == player)
         {
+            // Check that this player has not already confirmed, then they can't back out
+            if (m_kart_widgets[n].isReady())
+            {
+                sfx_manager->quickSound( SFXManager::SOUND_USE_ANVIL );
+                return true;
+            }
+            
             playerID = n;
             break;
         }