buffer: avoid creating the backing store in the thread

Fixes: nodejs#37030

PR-URL: nodejs#37052
Backport-PR-URL: nodejs#39704
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

src/node_blob.cc

@@ -253,8 +253,6 @@ 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;
@@ -313,6 +311,8 @@ 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();