OSV-2020-910 Use-of-uninitialized-value in zmq::stream_engine_base_t::out_event

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=24200 Crash type: Use-of-uninitialized-value Crash state: zmq::streamenginebaset::outevent zmq::epollt::loop zmq::workerpollerbaset::workerroutine...