PR6880: Don't dereference CallsExternalNode if it's NULL.

llvm-svn: 101897

llvm/lib/Analysis/IPA/CallGraph.cpp

@@ -158,9 +158,11 @@ private:
   // destroy - Release memory for the call graph
   virtual void destroy() {
     /// CallsExternalNode is not in the function map, delete it explicitly.
+    if (CallsExternalNode) {
       CallsExternalNode->allReferencesDropped();
       delete CallsExternalNode;
       CallsExternalNode = 0;
+    }
     CallGraph::destroy();
   }
 };