Make CreationContext() not crash when there is no creation context.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 0a785e613daa604b61106d28791913190e78dfba..065aa6e30ff23cd13ab082d167fccb2804262de6 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -6489,6 +6489,9 @@ Context* JSFunction::context() {
   return Context::cast(READ_FIELD(this, kContextOffset));
 }
 
+bool JSFunction::has_context() const {
+  return READ_FIELD(this, kContextOffset)->IsContext();
+}
 
 JSObject* JSFunction::global_proxy() {
   return context()->global_proxy();