Avoid crashing when checklines are incorrect

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@8818 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/tracks/check_manager.hpp

@@ -41,7 +41,10 @@ public:
     void reset(const Track &track);
     /** Returns the nth. check structure. */
     CheckStructure *getCheckStructure(unsigned int n) 
-                                                { return m_all_checks[n]; }
+    {
+        if (n >= m_all_checks.size()) return NULL;
+        return m_all_checks[n];
+    }
 };   // CheckManager
 
 #endif

src/tracks/check_structure.cpp

@@ -129,6 +129,8 @@ void CheckStructure::changeStatus(const std::vector<int> indices,
     {
         CheckStructure *cs = 
             m_check_manager->getCheckStructure(indices[i]);
+        if (cs == NULL) continue;
+        
         switch(change_state)
         {
         case CS_DEACTIVATE: