resolve gemini code review comments

Author: v-pratap

google/cloud/storage/internal/async/object_descriptor_impl.cc

@@ -65,10 +65,12 @@ void ObjectDescriptorImpl::Start(
 }
 
 bool ObjectDescriptorImpl::IsOpen() const {
-  std::unique_lock<std::mutex> lk(mu_);
-  if (cancelled_) return false;
-  if (stream_manager_->Empty()) return false;
-  return transport_ok_();
+  {
+    std::unique_lock<std::mutex> lk(mu_);
+    if (cancelled_) return false;
+    if (stream_manager_->Empty()) return false;
+  }
+  return !transport_ok_ || transport_ok_();
 }
 
 void ObjectDescriptorImpl::Cancel() {

google/cloud/storage/internal/async/object_descriptor_impl.h

@@ -126,7 +126,6 @@ class ObjectDescriptorImpl
       google::cloud::StatusOr<storage_internal::OpenStreamResult>>
       pending_stream_;
   bool cancelled_ = false;
-  bool permanent_failure_ = false;
   std::function<bool()> transport_ok_;
 };