Bugfix: beach track would crash.

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/branches/irrlicht@3307 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/graphics/irr_driver.cpp

@@ -83,7 +83,7 @@ IrrDriver::~IrrDriver()
 scene::IAnimatedMesh *IrrDriver::getAnimatedMesh(const std::string &filename)
 {
     scene::IAnimatedMesh *m = m_scene_manager->getMesh(filename.c_str());
-    setAllMaterialFlags(m);
+    if(m) setAllMaterialFlags(m);
     return m;
 }   // getAnimatedMesh