Better fix for cleanup on process termination.
Better fix for cleanup on process termination.

If `getpid` is None due to the module itself already being garbage
collected, it is reimported in order to be used in the cleanup logic.

This ensures that `zmq_term` is called when needed and still works
around missing global `getpid`.

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