server: Set the default thread exit code to 1.
The default exit code is only used when a process is killed by the system or through a signal. These are exceptional cases where exit code 1 (killed by Task Manager) is more appropriate than the normal termination code of 0.
Chromium does not restart helper processes that exit with code 0 (see kill.h), with this fix they are restarted when killed by the system or by a signal.