BUG/MEDIUM: stats: Get the right scope pointer depending on HTX is used or not

BUG/MEDIUM: stats: Get the right scope pointer depending on HTX is used or not

For HTX streams, the scope pointer is relative to the URI in the start-line. But
for streams using the legacy HTTP representation, the scope pointer is relative
to the beginning of output data in the channel's buffer. So we must be careful
to use the right one depending on the HTX is used or not.

Because the start-line is used to get de scope pointer, it is important to keep
it after the parsing of post paramters. So now, instead of removing blocks when
read in the function stats_process_http_post(), we just move on next, leaving it
in the HTX message.

Thanks to Pieter (PiBa-NL) to report this bug.

This patch must be backported to 1.9.