BUG/MINOR: mux-h1: Properly catch parsing errors on payload and trailers

Errors during the payload or the trailers parsing are reported with the
HTX_FL_PARSING_ERROR flag on the HTX message and not a negative return
value. This change was introduced when the fonctions to convert an H1 message to
HTX one were moved to a dedicated file. But the h1 mux was not fully updated

No backport needed except if the commits about file h1_htx.c are backported.
1 file changed