Fixed a problem VC++ revealed in release mode. Please verify.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@41996 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/AST/CFG.cpp b/AST/CFG.cpp
index 1f08e60..c89e580 100644
--- a/AST/CFG.cpp
+++ b/AST/CFG.cpp
@@ -1132,7 +1132,7 @@
         C->getRHS()->printPretty(OS);
       }
     }  
-    else if (DefaultStmt* D = dyn_cast<DefaultStmt>(D))
+    else if (DefaultStmt* D = dyn_cast<DefaultStmt>(S))
       OS << "default";
     else
       assert(false && "Invalid label statement in CFGBlock.");