[core] lighttpd -1 handles single request on stdin socket (fixes #1584)

[core] lighttpd -1 handles single request on stdin socket (fixes #1584)

(e.g. when called from xinetd)

Note: lighttpd is designed as a high performance, long-running server,
not a one-shot executable.  This one-shot mode of operation has not been
tuned for performance.  lighttpd server start-up and initialization aims
for correctness, not speed.  If using this one-shot mode as part of fork
and exec from xinetd, then performance is already not of high concern.

x-ref:
  "support for xinetd"
  https://redmine.lighttpd.net/issues/1584