Fix 100% CPU spin when --no-command is used (BZ#2492029)
socket_fd was declared as a global without an initializer, defaulting to 0. With --no-command, socket initialization is skipped, so socket_fd stays 0. The daemon loop checks if (socket_fd >= 0) and enters accept4(0, ...), spinning on stdin in a tight loop.
Fix: initialize socket_fd = -1.