Call zmq_stop only if there was a zmq_start [demos][skip hazardlib]
Call zmq_stop only if there was a zmq_start [demos][skip hazardlib]


Former-commit-id: f330adfacd9bd9576dd9dc4df01b4fa90c0635cd [formerly 3d6b6aba27ec422ac08446e0cf99114eebc6d78f]
Former-commit-id: 745d2e6aa4ac7f7027a1a31312273b6bca994b22
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine