add missing return in check_sys_un
add missing return in check_sys_un

Mustard-Systems-Ltd/pyzmq,caidongyun/pyzmq,swn1/pyzmq,ArvinPan/pyzmq,ArvinPan/pyzmq,Mustard-Systems-Ltd/pyzmq,dash-dash/pyzmq,Mustard-Systems-Ltd/pyzmq,caidongyun/pyzmq,swn1/pyzmq,dash-dash/pyzmq,caidongyun/pyzmq,yyt030/pyzmq,ArvinPan/pyzmq,yyt030/pyzmq,yyt030/pyzmq,dash-dash/pyzmq,swn1/pyzmq