Fix out-of-bounds access in fetching propery names

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index e63b9f7613d1a020c41156ad21bbccd4eb21ea49..51091bb4ada9f4f8ddedfe599ee4efa96a6ed7dd 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -4583,9 +4583,10 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_GetLocalPropertyNames) {
   // Get the property names.
   jsproto = obj;
   int proto_with_hidden_properties = 0;
+  int next_copy_index = 0;
   for (int i = 0; i < length; i++) {
-    jsproto->GetLocalPropertyNames(*names,
-                                   i == 0 ? 0 : local_property_count[i - 1]);
+    jsproto->GetLocalPropertyNames(*names, next_copy_index);
+    next_copy_index += local_property_count[i];
     if (jsproto->HasHiddenProperties()) {
       proto_with_hidden_properties++;
     }