message: fix: ensure json value is an array before pushing items
diff: @@ -15,6 +15,7 @@ namespace Nextclade {
  if (value->IsArray()) {
  auto a = rapidjson::MemoryPoolAllocator();
  rapidjson::Value result;
  + result.SetArray();
  for (auto&& item : value->GetArray()) {
  if (predicate(TreeNode{&item})) {
  result.PushBack(std::move(item), a);
  