Release the scgi task buffer on close

clear() keeps the capacity, and the task is pooled until exit.

src/rpc/scgi_task.cc

@@ -93,7 +93,8 @@ SCgiTask::close() {
   // The callbacks are guaranteed to be finished/canceled at this point.
   auto lock = std::lock_guard<std::mutex>(m_result_mutex);
 
-  m_buffer.clear();
+  // clear() would keep the capacity, and the task is pooled for the lifetime of the process.
+  std::vector<char>().swap(m_buffer);
 }
 
 void