bug 257188 - check initialization of nsThread patch by CTho <cst@andrew.cmu.edu> r=dougt

xpcom/threads/nsThread.cpp

@@ -263,6 +263,7 @@ nsThread::Init(nsIRunnable* runnable,
                PRThreadScope scope,
                PRThreadState state)
 {
+    NS_ENSURE_ARG_POINTER(runnable);
     mRunnable = runnable;
 
     NS_ADDREF_THIS();   // released in nsThread::Exit