StmtProfiler: Add a null check for child statements.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151812 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/StmtProfile.cpp b/lib/AST/StmtProfile.cpp
index 643bca8..d996925 100644
--- a/lib/AST/StmtProfile.cpp
+++ b/lib/AST/StmtProfile.cpp
@@ -69,8 +69,12 @@
 
 void StmtProfiler::VisitStmt(const Stmt *S) {
   ID.AddInteger(S->getStmtClass());
-  for (Stmt::const_child_range C = S->children(); C; ++C)
-    Visit(*C);
+  for (Stmt::const_child_range C = S->children(); C; ++C) {
+    if (*C)
+      Visit(*C);
+    else
+      ID.AddInteger(0);
+  }
 }
 
 void StmtProfiler::VisitDeclStmt(const DeclStmt *S) {