The end of http1_dissect_hdrs ends with skipping over the final [CR]LF
that marks then end of the headers. Currently that skip is optional, that
is, it is skipped if it was present.

This patch adds an assert if the final [CR]LF is not found when finishing
the parsing. HTTP1_Complete guarantees that it is there, if not we would
not have started parsing the request or response in the first place, and
if it is missing, there must be an error in the parsing leading up to it.