Bugfix: restarting a race could cause a crash in the skid marks.

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/trunk/supertuxkart@2581 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/graphics/skid_marks.cpp

@@ -56,6 +56,7 @@ void SkidMarks::reset()
     m_left.clear();
     m_right.clear();
     m_skid_marking = false;
+    m_current      = -1;
 }   // reset
 
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