buffer: avoid creating the backing store in the thread

Fixes: #37030

Author: jasnell

src/node_blob.cc

@@ -254,8 +254,6 @@ void FixedSizeBlobCopyJob::AfterThreadPoolWork(int status) {
 }
 
 void FixedSizeBlobCopyJob::DoThreadPoolWork() {
- Environment* env = AsyncWrap::env();
- destination_ = ArrayBuffer::NewBackingStore(env->isolate(), length_);
  unsigned char* dest = static_cast<unsigned char*>(destination_->Data());
  if (length_ > 0) {
  size_t total = 0;
@@ -314,6 +312,8 @@ void FixedSizeBlobCopyJob::Run(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  FixedSizeBlobCopyJob* job;
  ASSIGN_OR_RETURN_UNWRAP(&job, args.Holder());
+ job->destination_ =
+ ArrayBuffer::NewBackingStore(env->isolate(), job->length_);
  if (job->mode() == FixedSizeBlobCopyJob::Mode::ASYNC)
  return job->ScheduleWork();