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

src/wasm/wasm-module.cc

 // Copyright 2015 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.
 
 #include <memory>
 
 #include "src/assembler-inl.h"
 #include "src/base/adapters.h"
 #include "src/base/atomic-utils.h"
 #include "src/code-stubs.h"
@@ skipping 1933 matching lines @@
                 isolate_, table.min_size, maximum, &table_instance.js_wrappers);
           }
           desc.set_value(table_instance.table_object);
           break;
         }
         case kExternalMemory: {
           // Export the memory as a WebAssembly.Memory object.
           Handle<WasmMemoryObject> memory_object;
           if (!instance->has_memory_object()) {
             // If there was no imported WebAssembly.Memory object, create one.
-            Handle<JSArrayBuffer> buffer(instance->memory_buffer(), isolate_);
             memory_object = WasmMemoryObject::New(
-                isolate_, buffer,
+                isolate_,
+                (instance->has_memory_buffer())
+                    ? handle(instance->memory_buffer())
+                    : Handle<JSArrayBuffer>::null(),
                 (module_->max_mem_pages != 0) ? module_->max_mem_pages : -1);
             instance->set_memory_object(*memory_object);
           } else {
             memory_object =
                 Handle<WasmMemoryObject>(instance->memory_object(), isolate_);
             DCHECK(WasmJs::IsWasmMemoryObject(isolate_, memory_object));
             memory_object->ResetInstancesLink(isolate_);
           }
 
           desc.set_value(memory_object);
@@ skipping 1353 matching lines @@
                                      callee_compiled->instruction_start());
     }
     DCHECK_EQ(non_compiled_functions.size(), idx);
   }
 
   Code* ret =
       Code::cast(compiled_module->code_table()->get(func_to_return_idx));
   DCHECK_EQ(Code::WASM_FUNCTION, ret->kind());
   return handle(ret, isolate);
 }