Fix thread-safety when shutdown. (#1977)

Author: owent

ext/src/http/client/curl/http_client_curl.cc

@@ -253,7 +253,9 @@ void HttpClient::CleanupSession(uint64_t session_id)
       }
       else if (session->IsSessionActive() && session->GetOperation())
       {
-        session->FinishOperation();
+        // If this session is alread waiting to be removed, just wakeup background thread to call
+        // doRemoveSessions()
+        wakeupBackgroundThread();
       }
     }
   }