[views] fix ProcessInformationView: SESSION_MANAGER can be None (closes #5753280)
eg. with pyramid.
(grafted from 6a07c2dc3d85f4de0cf48221607e02c4473e11e4)
missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/share/pyshared/cubicweb/skeleton/debian/rules.tmpl)