Array<T>::attach() should copy size

c++/src/kj/array-test.c++

@@ -447,6 +447,7 @@ TEST(Array, AttachNested) {
   Array<Own<DestructionOrderRecorder>> combined = arr.attach(kj::mv(obj2)).attach(kj::mv(obj3));
 
   KJ_EXPECT(combined.begin() == ptr);
+  KJ_EXPECT(combined.size() == 1);
 
   KJ_EXPECT(obj1.get() == nullptr);
   KJ_EXPECT(obj2.get() == nullptr);

c++/src/kj/array.h

@@ -862,6 +862,7 @@ template <typename T>
 template <typename... Attachments>
 Array<T> Array<T>::attach(Attachments&&... attachments) {
   T* ptrCopy = ptr;
+  auto sizeCopy = size_;
 
   KJ_IREQUIRE(ptrCopy != nullptr, "cannot attach to null pointer");
 
@@ -872,7 +873,7 @@ Array<T> Array<T>::attach(Attachments&&... attachments) {
 
   auto bundle = new _::ArrayDisposableOwnedBundle<Array<T>, Attachments...>(
       kj::mv(*this), kj::fwd<Attachments>(attachments)...);
-  return Array<T>(ptrCopy, size_, *bundle);
+  return Array<T>(ptrCopy, sizeCopy, *bundle);
 }
 
 template <typename T>