[wasm] Handle no initial memory case correctly when memory is exported

src/wasm/wasm-objects.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_WASM_OBJECTS_H_
 #define V8_WASM_OBJECTS_H_
 
 #include "src/debug/debug.h"
 #include "src/debug/interface-types.h"
 #include "src/objects.h"
@@ skipping 84 matching lines @@
   // TODO(titzer): add the brand as an embedder field instead of a property.
   enum Fields : uint8_t {
     kWrapperTracerHeader,
     kArrayBuffer,
     kMaximum,
     kInstancesLink,
     kFieldCount
   };
 
   DECLARE_CASTS(WasmMemoryObject);
-  DECLARE_ACCESSORS(buffer, JSArrayBuffer);
+  DECLARE_OPTIONAL_ACCESSORS(buffer, JSArrayBuffer);
   DECLARE_OPTIONAL_ACCESSORS(instances_link, WasmInstanceWrapper);
 
   void AddInstance(Isolate* isolate, Handle<WasmInstanceObject> object);
   void ResetInstancesLink(Isolate* isolate);
   uint32_t current_pages();
   bool has_maximum_pages();
   int32_t maximum_pages();  // Returns < 0 if there is no maximum.
 
   static Handle<WasmMemoryObject> New(Isolate* isolate,
                                       Handle<JSArrayBuffer> buffer,
@@ skipping 544 matching lines @@
   };
 };
 
 #undef DECLARE_ACCESSORS
 #undef DECLARE_OPTIONAL_ACCESSORS
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_OBJECTS_H_