[web/debug] Fix check for open sessions
itervalues returns an iterator, which never evaluates to False.
Regression from 0bb18407c053 "[toward py3k] rewrite dict.keys() and
dict.values() (part of #2711624)".
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