fix broken build with old compilers, NFC
fix broken build with old compilers, NFC

daodaoliang/seafile-client,haiwen/seafile-client,wgaalves/seafile-client,lucius-feng/seafile-client,lucius-feng/seafile-client,daodaoliang/seafile-client,wgaalves/seafile-client,losingle/seafile-client,haiwen/seafile-client,lucius-feng/seafile-client,daodaoliang/seafile-client,haiwen/seafile-client,wgaalves/seafile-client,losingle/seafile-client,lucius-feng/seafile-client,haiwen/seafile-client,wgaalves/seafile-client,daodaoliang/seafile-client,losingle/seafile-client,losingle/seafile-client