[web] fix language negotiation
Regression caused by commit 6fd0ac6506cb "[web-request] handle default
language earlier". We would handle language negotiation at request
init time, but overwrite the selected language with the site default
when calling set_cnx.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html