[webrequest] Lazy-load search_state
- The update_search_state function will hit the session data only if __mode is
present in the form.
- set_search_state keep the same semantics
- Direct access to search_state in the session data is changed by an access to
the new property.
Closes #4875761
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