[core] fix triggered assert on HTTP chunked input (fixes #2822)
[core] fix triggered assert on HTTP chunked input (fixes #2822)

(thx AlxT)

x-ref:
  "Segmentation fault on HTTP chunked input"
  https://redmine.lighttpd.net/issues/2822

lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4