fix coredump

src/brpc/controller.cpp

@@ -765,9 +765,12 @@ void Controller::Call::OnComplete(Controller* c, int error_code/*note*/,
             sending_sock.get(), c, error_code);
     }
     if (enable_circuit_breaker) {
-        sending_sock->FeedbackCircuitBreaker(error_code, 
+        SocketUniquePtr sock; 
+        if (Socket::Address(peer_id, &sock) == 0) {
+            sock->FeedbackCircuitBreaker(error_code, 
                 butil::gettimeofday_us() - begin_time_us);
         }
+    }
     // Release the `Socket' we used to send/receive data
     sending_sock.reset(NULL);