fix：修正一个未置nullptr错误。

client/client.cpp

@@ -1217,6 +1217,7 @@ void CClient::handle_frame(CFrameBuffer* buf)
             break;
         }
         delete[] buf->data_;
+        buf->data_ = nullptr;
         msg_info.str = variable_and_reverse_files(msg_info.str);
         serialize(msg_info, &buf->data_, buf->len_);
         std::swap(buf->tid_, buf->fid_);