Win32: fixed cpu hog after process startup failure.

Win32: fixed cpu hog after process startup failure.

If ngx_spawn_process() failed while starting a process, the process
handle was closed but left non-NULL in the ngx_processes[] array.
The handle later was used in WaitForMultipleObjects() (if there
were multiple worker processes configured and at least one worker
process was started successfully), resulting in infinite loop.

Reported by Ricardo V G:
http://mailman.nginx.org/pipermail/nginx-devel/2012-July/002494.html