[d8] bounds-check before getting Shell::Worker internal field

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 7db6f3ed9e442081528e05140bd25b8911e26cb6..2117825ef4b77b5f89d66934bd3471086e42fd12 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -717,14 +717,17 @@ void Shell::WorkerPostMessage(const v8::FunctionCallbackInfo<v8::Value>& args) {
   Isolate* isolate = args.GetIsolate();
   HandleScope handle_scope(isolate);
   Local<Context> context = isolate->GetCurrentContext();
+  Local<Value> this_value;
 
   if (args.Length() < 1) {
     Throw(isolate, "Invalid argument");
     return;
   }
 
-  Local<Value> this_value = args.This()->GetInternalField(0);
-  if (!this_value->IsExternal()) {
+  if (args.This()->InternalFieldCount() > 0) {
+    this_value = args.This()->GetInternalField(0);
+  }
+  if (this_value.IsEmpty()) {
     Throw(isolate, "this is not a Worker");
     return;
   }
@@ -770,9 +773,11 @@ void Shell::WorkerPostMessage(const v8::FunctionCallbackInfo<v8::Value>& args) {
 void Shell::WorkerGetMessage(const v8::FunctionCallbackInfo<v8::Value>& args) {
   Isolate* isolate = args.GetIsolate();
   HandleScope handle_scope(isolate);
-
-  Local<Value> this_value = args.This()->GetInternalField(0);
-  if (!this_value->IsExternal()) {
+  Local<Value> this_value;
+  if (args.This()->InternalFieldCount() > 0) {
+    this_value = args.This()->GetInternalField(0);
+  }
+  if (this_value.IsEmpty()) {
     Throw(isolate, "this is not a Worker");
     return;
   }
@@ -795,8 +800,11 @@ void Shell::WorkerGetMessage(const v8::FunctionCallbackInfo<v8::Value>& args) {
 void Shell::WorkerTerminate(const v8::FunctionCallbackInfo<v8::Value>& args) {
   Isolate* isolate = args.GetIsolate();
   HandleScope handle_scope(isolate);
-  Local<Value> this_value = args.This()->GetInternalField(0);
-  if (!this_value->IsExternal()) {
+  Local<Value> this_value;
+  if (args.This()->InternalFieldCount() > 0) {
+    this_value = args.This()->GetInternalField(0);
+  }
+  if (this_value.IsEmpty()) {
     Throw(isolate, "this is not a Worker");
     return;
   }